Due diligence is the 45–60 day window between signing an LOI and closing a deal. In theory, it exists so buyers can verify that what the seller represented is true. In practice, it is the single most important risk management tool in a business acquisition — and the place where the difference between prepared buyers and unprepared buyers is most visible. Prepared buyers arrive with a complete document request list, a tracking system, clear milestones, and experienced advisors. Unprepared buyers arrive with a vague list, no timeline, and a belief that the seller will tell them everything important. The latter group closes deals they should not close — or misses issues that become expensive after the wire is sent. This checklist covers every major diligence category, with specific items to request and the signals to watch for.
How to Run Due Diligence Like a Project, Not a Checklist
The most important thing you can do to improve the quality of your due diligence is to treat it as a project with a timeline, milestones, and a single owner — not as a checklist you work through passively as documents arrive. Buyers who manage diligence as a project consistently close better deals than buyers who wait for the seller to tell them what to look at.
Before you send your first document request, create a master diligence tracker: a spreadsheet with every item you need, the category it belongs to, who is responsible for requesting and reviewing it, the date requested, and the date received. Share this tracker with the seller at the start of diligence so both parties have the same visibility into what is needed and by when. Sellers who have nothing to hide respond quickly and completely. Sellers who are slow, vague, or repeatedly unable to produce requested documents are giving you information about how the business is actually run.
Set milestone dates within your exclusivity period: financial review complete by Day 14, legal review by Day 30, management interviews by Day 35, all advisors' reports by Day 42, purchase agreement draft by Day 50. Build your SBA lender into the timeline — if you are using SBA financing, the lender needs to be engaged on Day 1, not after you finish diligence. Running lender and legal diligence in parallel rather than sequentially is the single most effective way to avoid timeline overruns.
Financial Due Diligence — The Foundation
Financial diligence starts with reconciling three years of federal tax returns against three years of financial statements. These two documents should tell the same story. When they do not — when the P&L shows significantly higher revenue or EBITDA than the tax return — you need to understand the discrepancy completely before you can price the deal.
Request and review: three years of federal and state income tax returns, three years of accrual-basis profit and loss statements and balance sheets, monthly revenue reports for the last 24 months, accounts receivable and payable aging schedules, and the seller's complete add-back schedule with documentation for every claimed adjustment. Every add-back should be documented with receipts, payroll records, or bank statements. Undocumented add-backs that you accept in the LOI will create disputes during lender underwriting when the documentation cannot be produced.
Look specifically for: revenue that is growing on the P&L but flat or declining on tax returns (a timing discrepancy at minimum, a truthfulness question at worst), owner compensation that was above market for the years being presented (a legitimate add-back if documented), large one-time expenses that recur under different line items every year (not one-time), and cash deposits that do not appear in reported revenue. For healthcare businesses like dental practices and home health agencies, also request the payer mix breakdown and any accounts receivable by payer — Medicare and Medicaid receivables age differently than commercial insurance and materially affect working capital.
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Once you have verified EBITDA, use the Valuation Estimator to calculate a defensible purchase price range based on industry multiples.
Estimate deal value →Revenue Quality and Customer Due Diligence
Not all revenue is equal, and the difference between recurring contracted revenue and transactional project revenue can shift a multiple by 1–2x. Your customer due diligence should quantify the quality of the revenue you are buying, not just its volume.
Request a customer revenue schedule showing the top 20–30 customers by revenue for each of the last three years. Look for: any customer representing more than 20% of revenue (concentration risk), customers whose spend has declined year-over-year (early churn signal), customers whose contracts expire within 12 months of close (contract rollover risk), and customers who are personal relationships of the seller rather than institutional relationships of the business (key-man transfer risk).
For recurring revenue businesses — veterinary practices with wellness plan subscribers, landscaping companies with maintenance contracts, physical therapy clinics with payer agreements — request contract terms, renewal history, and any volume commitments. Ask the seller to explain which customer relationships they personally manage versus those managed by other staff. A seller who manages 80% of the top 10 customer relationships personally is a seller who is taking significant value with them when they leave — value that needs to be mitigated through earnout structures, extended transition agreements, or a reduced purchase price.
Operational Due Diligence
Operational diligence answers one question: can this business generate the same results under your ownership as it does under the current owner? If the answer requires the seller to remain involved, that involvement needs to be contracted and priced. If the answer is no under any scenario — because the seller is the sole reason customers buy from the business — that is a fundamental risk that affects both price and structure.
Request: a complete org chart with names, roles, tenure, and compensation, employment agreements for key staff, operating procedures for core business processes (customer acquisition, service delivery, billing, scheduling), technology systems currently in use and their associated contracts, equipment list with make, model, year, and condition, and a written seller assessment of which employees would likely leave if a sale became known.
For businesses where the owner holds professional licenses — HVAC companies and plumbing businesses are the most common examples in home services — verify that there are licensed technicians on staff who can legally operate and sign off on work post-close, and that their licenses are current and will remain with the business. A business where the owner is the only licensed contractor is a business that cannot legally operate if the owner exits without a transition period — which creates deal structure requirements that should be addressed before the purchase agreement is finalized.
Legal Due Diligence — Contracts, Licenses, and Liabilities
Legal diligence should be led by an M&A attorney, but you need to understand what they are looking for so you can ask intelligent questions and prioritize your advisory time. The four primary legal categories are material contracts, licenses and permits, litigation history, and intellectual property.
For material contracts, request all customer contracts (flag any with change-of-control provisions — these may be invalidated by an acquisition), all vendor and supplier agreements, equipment financing agreements, real estate leases, and any non-compete or non-solicitation agreements currently in effect for the business. A change-of-control clause in a contract with a customer representing 25% of revenue is a potential deal-breaker. Identify these early, not during purchase agreement negotiation.
For licenses and permits, request a complete list of all licenses held by the business and confirm their transferability. In regulated industries — pest control companies with state applicator licenses, home health agencies with Medicare and Medicaid certifications, healthcare practices with facility licenses — licensing transferability is frequently the longest lead-time item in the acquisition. Start the licensing investigation in the first week of diligence, not the last.
Employee and HR Due Diligence
Employment liability is one of the most common sources of post-close surprises because it is invisible in financial statements. A misclassified workforce, an unresolved wage claim, or an employee who was wrongfully terminated six months before close may not appear anywhere in the seller's financials — but can produce material liability that transfers to you as the new owner if not properly addressed in the purchase agreement.
Request: a complete employee roster with names, titles, compensation (salary, hourly rate, benefits), start dates, and classification (W-2 employee or 1099 contractor), copies of all employment agreements and offer letters, documentation of any past or pending HR claims, EEOC complaints, or labor department investigations, and the employee handbook and leave policies.
Worker classification is the highest-risk area in most service business acquisitions. Businesses that routinely use 1099 contractors for work that meets the IRS or state definition of employment carry significant liability — back taxes, penalties, and potential state labor department claims — that may transfer to you as the buyer depending on how the purchase agreement is structured. This risk is elevated in industries with large field workforces: commercial landscaping companies, HVAC businesses, and similar businesses should be scrutinized carefully on this point. Require a warranty from the seller in the purchase agreement that all workers are correctly classified, with indemnification for any pre-close classification claims.
Technology and Systems Due Diligence
Technology diligence is underweighted by most first-time buyers, who tend to think of small businesses as low-tech. But the operational systems a business runs on — scheduling software, CRM, ERP, billing, dispatch, customer communication — are infrastructure that a new owner will rely on from Day 1. Understanding what they are, what they cost, and whether they will continue under new ownership is not optional.
Request a complete inventory of all software systems in use, including vendor names, monthly or annual costs, contract terms, and whether the contracts are in the business's name or the owner's personal name. Software contracted under the seller's personal account — common in small businesses that grew without a systematic IT approach — may not transfer automatically at close. Check each major system for: change-of-ownership provisions, auto-renewal dates within 6 months of closing, and any provisions that could allow the vendor to increase pricing or change terms upon ownership transfer.
Also assess the business's data quality. Does the CRM contain complete, accurate customer contact information? Are financial records maintained in a system that produces clean reports, or is the accounting a mess that only the seller understands? A business where customer records are in the owner's personal phone contacts and financial records require the owner's interpretation is a business with an operational key-man risk that extends beyond the customer relationships themselves. This risk needs to be quantified in the transition period and addressed in the consulting agreement.
Environmental and Real Estate Due Diligence
For businesses that operate from physical locations — especially those that handle chemicals, fuel, vehicles, or industrial equipment — environmental due diligence is not optional. Contaminated property transfers with the ownership of the contaminating business in certain deal structures, and cleanup costs can run into the hundreds of thousands of dollars.
For businesses that own or lease commercial real estate, request the current lease with all amendments, the lease expiration date and renewal options, and the landlord consent requirements for assignment. A lease that expires 18 months after close with no renewal option is a material business risk. A lease with a change-of-control provision that requires landlord consent before assignment can delay or complicate closing. And a landlord who uses the sale as leverage to renegotiate the lease can materially change the cost structure of the business you are buying.
If the business operates from a facility that has ever stored fuel, solvents, pesticides, or industrial chemicals — auto repair shops, pest control depots, HVAC suppliers with refrigerant storage — request a Phase I environmental site assessment from an independent environmental consultant. A Phase I is a records review and site inspection, not a full soil and water test. If the Phase I identifies concerns, a Phase II (actual sampling) may be warranted. The cost of a Phase I ($1,500–$3,000) is trivial relative to the cost of discovering contamination after close.
Insurance Due Diligence
Insurance review is a routine diligence item that most buyers treat as a box to check. A more useful approach is to review the current policies as a risk map — what risks does the business face, which ones are currently covered, which ones are underinsured, and which ones will require new policies under your ownership?
Request copies of all current insurance policies: general liability, workers compensation, commercial auto (critical for any business with a vehicle fleet), professional liability or errors and omissions (important for professional service businesses), property insurance, and any umbrella or excess liability policies. Also request the loss run reports for the last five years — these show claims history and tell you whether the business has a pattern of incidents that the current premiums are pricing.
Confirm that all policies are in the business's name (not the owner's personal name) and will be transferable or replaceable at close. Some specialty coverage — professional liability in healthcare, for example — requires new applications and underwriting under the new owner. Start those applications early. Also verify that the seller's current coverage levels meet any contractual minimums in customer or vendor contracts, particularly commercial accounts that specify minimum insurance requirements.
Integration Planning During Due Diligence
Most buyers treat integration planning as something that happens after close. The buyers who experience the smoothest transitions are those who use the diligence period to build their integration plan, not just to validate the acquisition thesis. By Day 45 of diligence, you know enough about the business to plan the first 90 days of ownership — and you should.
Use the operational diligence findings to identify: the three or four employees who are most critical to business continuity and how you will ensure their retention post-close, the top 10 customers who need a personal introduction from the seller before the deal becomes public, the operational processes that are currently in the seller's head and need to be documented before they leave, and the systems or workflows that are held together with informal knowledge and need to be formalized.
Write a Day 1 playbook before you close. What will you communicate to employees on the first morning? What will you communicate to customers, and through what channel? What will stay exactly the same for the first 90 days (pricing, service offerings, team structure, billing), and what will you evaluate before changing? The businesses that retain their highest-value customers and employees through transitions are those where the new owner arrived with a clear, communicated plan — not those where employees and customers had to guess what was changing and why.
Every post-close surprise was a pre-close warning that someone missed or chose to ignore. The purpose of due diligence is not to find reasons to kill deals — it is to understand exactly what you are buying before you are legally obligated to buy it. Run diligence as a project. Use qualified advisors. Follow the timeline. And treat the seller's responsiveness to document requests as data, not just logistics. The combination of thorough preparation and direct observation during the diligence period is the most reliable way to close a deal that performs the way you modeled it.
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