Due Diligence, Demystified
The Hook
Due diligence is where exciting deals quietly die, and where smart buyers find the price was a fantasy. It is not paperwork. It is the systematic act of checking whether the story you were sold is actually true. Learn the four lenses and you will never again nod along to a number you have not tested.
Plain English
Due diligence is the deep investigation a buyer runs before closing a deal, to confirm the business is worth what they are about to pay and to surface anything that could blow up later. Think of it as opening every drawer in a house you are about to buy, not just admiring the kitchen. It usually begins after both sides sign a non-disclosure agreement (NDA), which is the legal promise that the confidential information being shared stays private. The work is organized into four lenses. Financial diligence checks whether the earnings are real and repeatable. Legal diligence checks who actually owns what and what liabilities are hiding in contracts. Commercial diligence checks whether the customers, market, and growth story hold up. Technical diligence checks whether the technology, systems, or operations are sound and not held together with tape. Each lens can kill a deal on its own, and the most expensive mistakes come from skipping one because the other three looked fine.
The Math
Due diligence is structural, so the framework matters more than a single equation. The discipline is to run all four lenses, because a deal that passes three and fails one can still be a disaster. The one number people fixate on is Quality of Earnings (QofE), which tests whether reported profit is real, recurring cash earnings or whether it has been inflated by one-time items, aggressive accounting, or owner perks that will not continue.
- The four lenses: Financial (are the earnings real?), Legal (who owns what and what is owed?), Commercial (will customers and the market hold?), Technical (do the systems and operations actually work?)
- Adjusted earnings (QofE) = reported EBITDA + one-time costs that will not recur - one-time gains that will not recur - owner perks being added back that a new owner must still pay
- Customer concentration check = revenue from the largest customer / total revenue (a high number is a flashing red light)
A seller reports EBITDA of 5,000,000 dollars and asks for a price of 6 times earnings, or 30,000,000 dollars. Financial diligence opens the drawers. It finds a one-time legal settlement gain of 800,000 dollars baked into the profit (it will not happen again, so it comes out). It finds the owner pays herself 200,000 dollars below market, so a new owner must add 200,000 dollars of real salary cost (that comes out too). It finds 400,000 dollars of genuinely one-time consulting fees that will not recur (those get added back). Adjusted earnings = 5,000,000 - 800,000 - 200,000 + 400,000 = 4,400,000 dollars. At the same 6 times multiple, the defensible price is 26,400,000 dollars, not 30,000,000. Diligence just found 3,600,000 dollars.
A software company sails through financial diligence: clean books, growing revenue, healthy margins. Then commercial diligence runs the customer concentration check. One client accounts for 6,000,000 dollars of the company's 10,000,000 dollars in revenue, so concentration = 6,000,000 / 10,000,000 = 60 percent. That single customer is on a contract that expires in eight months with no renewal signed. The earnings are real today, but 60 percent of them rest on one relationship that could vanish. The financial lens said yes. The commercial lens said proceed with extreme caution. This is exactly why you run all four, never just the one that flatters the deal.
A manufacturing target looks great financially and commercially. Legal diligence reads the fine print and finds the company does not actually own the patent it markets as its core advantage. It licenses the patent, and the license expires in two years with a renewal price the owner can set. Technical diligence inspects the factory and finds the main production line needs 2,500,000 dollars of capital spending within 18 months just to keep running. Neither problem shows up in the income statement today. Together they reset the buyer's offer: lower the price, add a clause that holds back funds until the patent risk is resolved, or walk. The lesson is that the most dangerous numbers in a deal are the ones not yet on any statement.
The Lingo
- Due diligence
- The buyer's deep investigation before closing, to confirm value and surface risks across financial, legal, commercial, and technical lenses.
- Quality of Earnings (QofE)
- An analysis that tests whether reported profit is real, recurring cash earnings or inflated by one-time items and accounting choices.
- Non-disclosure agreement (NDA)
- The legal agreement that lets both sides share confidential information while promising to keep it private.
- Data room
- The secure (usually online) repository where the seller posts documents for the buyer's diligence team to review.
- Customer concentration
- How much of total revenue depends on one or a few customers. High concentration is a major risk.
- Add-back
- A cost removed from reported earnings during QofE because it is one-time or will not continue under new ownership.
- Representations and warranties
- The seller's formal statements that facts about the business are true, which the buyer can rely on and enforce.
Practice
In the Room
The Trap
Treating due diligence as a checklist to clear rather than a real investigation, and trusting the seller's numbers because the books look tidy. The most expensive deals fail on the lens nobody bothered to run, often commercial or technical, while everyone admired clean financials. Run all four lenses, demand a Quality of Earnings on the profit, and ask one blunt question of every number: is this real, and will it still be true after we own it?
Quick Check
Q1.What is the purpose of a Quality of Earnings analysis?
Q2.Why should a buyer run all four diligence lenses instead of just the financial one?
Q3.Reported EBITDA is 5,000,000 dollars. Diligence removes an 800,000 dollar one-time gain and removes 200,000 dollars for a below-market owner salary, then adds back 400,000 dollars of truly one-time fees. What is adjusted earnings?
Q4.One customer provides 6,000,000 dollars of a company's 10,000,000 dollars in revenue. What is the customer concentration, and what does it signal?
Q5.What does signing an NDA at the start of diligence accomplish?
Practice Out Loud
A partner wants to close quickly on a target with clean-looking financials and a great growth story. In 60 seconds, explain which diligence lenses you would still insist on running and why one passing lens is not enough. The AI will play a deal lead who pushes back: the books are spotless, why are we slowing this down?
Try it in real life
This week, pick one company you follow and find one real world example of due diligence, demystified. Write down what you noticed in two sentences.
Wrap up this lesson
Submitting the Quick Check counts. Or mark it here when you feel ready.