Due diligence is the 30–60 day period between signing an LOI and closing a deal. Done right, it protects you from overpaying, surfaces risks the seller may not have disclosed, and gives you the information you need to negotiate a final purchase price and deal structure with confidence. Done poorly, it creates false certainty — and post-close surprises that can sink an otherwise good acquisition. This checklist covers every major diligence category, with specific items to request and the red flags to watch for in each.
Financial Due Diligence — The Foundation of Everything
Financial diligence starts with reconciling three years of 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 why before you get any further.
Request: federal and state tax returns for 3 years, accrual-basis P&Ls and balance sheets for 3 years, monthly revenue reports for the last 24 months, accounts receivable and payable aging, and the seller's add-back schedule with documentation for every adjustment. Scrutinize every add-back. Buyer-side add-back analysis is the most common source of purchase price disagreements.
Red flags: revenue that is growing on the P&L but flat or declining on tax returns; high owner compensation that vanishes in the adjusted EBITDA without clear market-rate replacement costs; large one-time add-backs that recur every year under different line items.
Industry Due Diligence Guides
See detailed due diligence checklists for specific industries including HVAC, urgent care, and septic services.
View industry checklist →Revenue Quality and Customer Concentration
Not all revenue is equal. A business with 80% of revenue concentrated in three customers is a fundamentally different risk profile than a business with 200 recurring customers where no single customer exceeds 8% of revenue. Buyers pay premium multiples for revenue diversification — and apply steep discounts for concentration.
Request a customer revenue schedule showing the top 20 customers by revenue for each of the last three years. Look for: (1) any customer that represents more than 20% of revenue; (2) customers who have reduced spend year-over-year; (3) customers whose contracts expire within 12 months of close; and (4) customers that are personal relationships of the seller rather than institutional relationships of the business.
For recurring revenue businesses, also request: contract terms and renewal history, churn rate by cohort, and average revenue per customer trend over 3 years. Recurring revenue that is declining in quality — through customer churn or contract downsizing — is often masked in aggregate revenue growth.
Operational Due Diligence — The Business Behind the Numbers
Operational diligence answers one question: can this business run without the current owner? If the answer is no — if the owner is the primary salesperson, the key technician, and the person customers call directly — you are acquiring a job, not a business.
Request: an org chart with roles and tenure, employment agreements for key staff, compensation schedules, and the seller's honest assessment of who would leave if the deal became known. Schedule site visits and speak directly with key employees (with seller consent) to understand their commitment and their view of the business's strengths and challenges.
Also request: documented operating procedures for core business processes, any technology systems (CRM, ERP, scheduling software) and their current usage, customer onboarding and service delivery workflows, and equipment lists with age and condition. The goal is to understand what institutional knowledge lives in documents and systems versus in the seller's head.
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. The primary categories are: material contracts, licenses and permits, litigation history, and intellectual property.
For material contracts, request all customer contracts (especially any with change-of-control provisions), vendor and supplier agreements, lease agreements, equipment financing, and any non-compete or non-solicitation agreements currently in effect. Change-of-control clauses in key customer contracts can invalidate those contracts upon acquisition — a deal-breaking issue if those customers represent significant revenue.
For licenses and permits, verify that the business holds all required licenses for its operations and that those licenses are transferable. In regulated industries — healthcare, childcare, environmental services, financial services — licensing transferability is often the longest lead-time item in the deal. Start this investigation early.
Employee and HR Due Diligence
Employment liability is one of the most common sources of post-close surprises. Request: a complete employee roster with titles, compensation, start dates, and classification (W-2 vs 1099), copies of all employment agreements and offer letters, documentation of any past or pending HR claims or EEOC complaints, and the business's employee handbook and leave policies.
Pay particular attention to worker classification. Businesses that routinely misclassify employees as independent contractors carry significant IRS and state labor department liability — liability that may transfer to you as the buyer if not properly structured in the purchase agreement.
How to Organize Your Due Diligence Process
The buyers who complete diligence most effectively are those who organize it as a project, not a document request. Create a master diligence tracker — a spreadsheet with every item you need, who is responsible for requesting it, the date requested, and the date received. Share this tracker with the seller at the start of diligence so both parties understand what is needed and by when.
Set milestone dates within your diligence period: financial review complete by Day 14, legal review complete by Day 30, management interviews by Day 35, final report by Day 42. If the seller is not providing documents on schedule, that is itself a data point. Sellers who have clean operations and nothing to hide tend to produce documents quickly.
Consider using a virtual data room (VDR) for organizing and sharing documents securely. Free or low-cost VDR tools exist, and they create a cleaner audit trail than email chains. For deal structure resources, the Deal Structure Builder can help you model how your diligence findings affect the purchase price and financing structure.
Due diligence is not about finding reasons to kill a deal — it is about understanding what you are buying well enough to price it correctly and structure it to protect you. The best buyers approach diligence as a value creation tool: every risk you surface during diligence is either a negotiating point, a post-close improvement opportunity, or a genuine reason to walk away. All three outcomes are valuable.
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