Due Diligence Checklist for Buying a Business

Due diligence checklist overview

Buying a business is one of the largest financial decisions you will ever make. Due diligence is the process that determines whether you are actually getting what you paid for. It is your opportunity to verify financials, uncover hidden risks, and build the confidence you need to close, or walk away.

This due diligence checklist for buying a business is written specifically for buyers in the lower middle market, covering deals in the $1 million to $25 million range. Whether you are a first-time acquirer or an experienced operator, use this guide to structure your review, align with your advisors, and protect your investment.

What is due diligence?

Due diligence is the structured process of verifying everything a seller has represented about their business before you commit to closing. It covers financials, operations, legal standing, employees, customers, and market position.

There are three core purposes behind business acquisition due diligence:

1. Confirm the accuracy of the financials presented during the sale process
2. Understand the risks and benefits of the business as it actually operates
3. Justify the purchase price and satisfy the requirements of your lender

Due diligence typically involves your attorney, CPA or accountant, and in many cases an M&A advisor or business broker. Most organized sellers, particularly those working with advisors, will prepare a data room in advance with documents pre-organized by category. Request one early in the process.

Keep in mind that no two deals are identical. Buyers often receive a boilerplate checklist, but not every item applies to every transaction. Use this guide as a comprehensive starting point, then filter based on deal structure, industry, and business model.

When due diligence begins

Due diligence begins immediately after the Letter of Intent (LOI) is signed. The LOI will include contingency language that makes the deal conditional on your satisfaction with due diligence findings. A typical LOI clause reads something like: "This offer is contingent upon Buyer's satisfactory completion of due diligence within 45 days of the execution of this Letter of Intent."

One critical point: due diligence runs simultaneously with drafting and negotiating the Definitive Agreement, which makes speed essential. "Time kills deals" is a phrase you will hear from every experienced M&A advisor, and it is true. Deal fatigue from a prolonged due diligence process is one of the primary reasons acquisitions fall apart before closing.

Set clear milestones at the start, establish a document request list immediately, and keep your advisors aligned and moving.

Financial due diligence

Financial due diligence is the most critical component of any business acquisition checklist. Your goal is to verify that the revenues, expenses, and profits presented during the sale process are accurate, consistent, and sustainable.

What to analyze in financial due diligence

EBITDA and addbacks. Most lower middle market businesses are valued on a multiple of EBITDA. Verifying each addback is a critical step. A seller's salary is a valid addback if they are departing, but it must be quantifiable and documented via tax return, payroll journal, or W-2. Challenge any addback that cannot be independently verified. For industry-specific benchmarks, see EBITDA multiples by industry to understand what ranges are typical for the sector you are acquiring in.

Revenue trends and margin changes. Watch for sudden margin improvements in the most recent period without a clear business explanation. This can signal financial manipulation designed to inflate the sale price.

Cash basis accounting risk. A seller operating on a cash basis can appear more profitable simply by delaying bill payments. Cross-check the accounts payable report carefully to identify any buildup of unpaid obligations.

Bank deposit reconciliation. Have your CPA reconcile bank deposits against reported revenue. Request IRS tax transcripts directly to independently verify that filed tax returns match what the seller has provided to you.

Revenue pulled forward. Sellers sometimes offer customers discounts before closing to accelerate cash receipts, which inflates near-term revenue but creates a trough post-closing. Request monthly sales reports for the 12 to 24 months leading up to the sale and investigate any unexplained revenue spikes.

Revenue and customer due diligence

Revenue quality matters as much as revenue quantity. A business generating $5 million in revenue from two clients is a fundamentally different risk profile than one generating the same revenue from 200 clients. This section of your due diligence checklist evaluates whether the revenue is durable.

Stress test high concentration. If the top 3 customers account for more than 35% of total revenue, model what happens if two of them leave on Day 1 of your ownership. Can the business still service its debt and cover operations? If not, that concentration risk should be reflected in your offer price or deal structure.

Meet key customers directly. Where possible, ask the seller to introduce you to their top customers. Having the seller call a key customer with you on the phone helps you assess the relationship and whether it is tied to the seller personally or to the business itself.

Protect yourself with deal structure. If a key customer relationship is a meaningful driver of value, consider negotiating a seller note tied to that customer's retention. If the customer leaves post-close, a portion of the note is forgiven to right-size the purchase price.

Operational due diligence

Operational due diligence confirms that the business actually runs the way it has been described, and that there are no hidden dependencies, supply chain vulnerabilities, or deferred maintenance issues that will cost you money after closing.

Never skip the physical equipment inspection. Verify that every asset listed in the purchase agreement actually exists, is in working condition, and matches the age and value represented. A verified equipment list signed by both parties should be attached as an exhibit to your purchase agreement.

For inventory-heavy businesses, confirm that inventory is salable and not obsolete. Slow-moving or dead inventory sitting on the balance sheet can inflate working capital calculations and leave you holding assets with little resale value.

Legal due diligence

Legal due diligence protects you from inheriting liabilities, losing critical operating rights, or discovering after closing that a key contract is non-transferable. Your attorney should lead this workstream.

Pay close attention to licenses and permits. If any license required to operate the business is held personally by the seller rather than the business entity, it may not transfer with the sale. This can create an immediate operational problem on Day 1.

In an asset purchase, confirm which contracts require third-party consent to assign. A landlord, key supplier, or major customer may have the right to terminate their agreement upon a change of ownership, which can materially affect the value you are paying for.

Employee and HR due diligence

People risk is one of the most underestimated categories in small business acquisition due diligence. Understanding who holds key relationships, technical knowledge, and operational expertise, and whether they will stay post-close, is essential to protecting the business you are buying.

If the seller is the primary holder of customer relationships or proprietary knowledge, plan your transition accordingly. A seller note or earnout tied to a defined transition period can incentivize the seller to actively support knowledge transfer and customer introductions after closing, rather than simply cashing out and walking away.

Consider retention bonuses for key employees. The cost of retaining a critical operations manager or top salesperson is almost always lower than the cost of replacing one post-close.

Assets and liabilities

Confirming exactly what you are buying and what obligations you are inheriting prevents expensive surprises after closing. This section is especially important in deals where the purchase structure, asset purchase versus stock purchase, affects what transfers to you.

Working capital matters at closing. In a stock purchase, a working capital target or "peg" is typically negotiated as part of the deal. If working capital at closing falls below the target, the purchase price is reduced. If it exceeds the target, the price may increase. Getting this right protects both parties and prevents the seller from draining the business of cash before closing.

Accounts receivable in asset purchases. If the seller retains accounts receivable in an asset purchase, you will need additional cash on Day 1 to fund the balance sheet gap. Factor this into your offer and your financing discussions with your lender.

Market and industry due diligence

Understanding the external environment the business operates in helps you assess whether historical performance is repeatable and whether the business is positioned for future growth or facing structural headwinds.

Lenders evaluate cyclicality carefully. Businesses tied to new housing starts, for example, are often viewed as higher risk due to their sensitivity to economic downturns. If your target operates in a cyclical sector, your lender will scrutinize this closely, and so should you.

Run a debt service stress test. Identify the revenue and margin level at which the business can no longer cover its debt obligations, then ask whether a realistic downturn could get you there. If the answer is yes, revisit your price or your financing structure before proceeding. For a deeper look at how to approach valuation from a buyer's perspective, see how to value a company for purchase.

Seller dependency

One of the most commonly underestimated risks in lower middle market acquisitions is how dependent the business is on the seller as an individual. A business that requires the seller to run is not as valuable as one that operates independently.

Ask directly why the seller is selling. The answer matters. A seller approaching retirement with a clean, well-documented business is a very different situation from a younger seller who claims to be leaving for "other interests." Investigate closely when the stated reason does not clearly align with the seller's profile and circumstances.

A non-compete agreement with the seller is not optional. It should be included in your purchase agreement and clearly define geography, duration, and the scope of restricted activity.

Red flags to watch for

No due diligence checklist for buying a business is complete without a direct list of warning signs. These are the issues that most often indicate a deal is mispriced, misrepresented, or simply not worth pursuing.

Any one of these issues may be explainable in isolation. A pattern of two or more is a serious problem. When a seller is reluctant to provide access, that reluctance itself is the most important data point you will receive.

Professional advisors to involve

Business acquisition due diligence is a team effort. Attempting to complete it without qualified advisors increases your risk substantially, particularly in the lower middle market where deals often involve complex financial structures, SBA financing, and negotiated deal terms.

Your lender will conduct their own independent verification of the financials. Aligning your due diligence findings with what your lender is seeing protects you from surprises late in the process. If your CPA's EBITDA calculation and the lender's do not match, identify the discrepancy before it becomes a problem at closing.

If you are sourcing a deal through a marketplace like Dealflow.com, take advantage of access to vetted M&A advisors, lenders, and sellers who provide organized due diligence packages. Working with professionals who understand lower middle market deal mechanics can significantly reduce the time and risk involved in closing your acquisition. If you are still evaluating which types of buyers you may be competing against, reviewing the 6 groups that could buy your business can help you understand the competitive landscape from a seller's perspective.