What Due Diligence Cannot See
And Why That Gap Shapes Everything That Comes After
The Integration Playbook | Article 2 of 9 | This series examines the seven decisions that determine whether an environmental firm acquisition delivers value. Start with Article 1 here.
I was sitting in on a deal a few years back where the firm being acquired kept circling back to the same set of questions. They asked about technical problem-solving on complex projects. They asked about keystone work the acquirer was known for. They asked about the tenure and credentials of the technical staff. Different framings, same underlying question, asked repeatedly across multiple conversations.
The questions were not random. They revealed a culture, surfacing through the things this firm could not stop asking about. Deep technical expertise was what they valued most, and they were testing whether they were about to lose it.
What a firm keeps asking about tells you what they are afraid of losing. And due diligence, done honestly, is not just the acquirer evaluating the seller. Both firms are evaluating each other, and the structure of the process makes that hard for everyone.
The Information Problem
Every acquisition begins with an information problem. The acquirer needs to learn enough about the target firm to justify the price, plan the integration, and protect against surprises. The target firm needs to learn enough about the acquirer to know what they are signing up for. Neither side can fully accomplish this before close, and the structural reasons why are worth reviewing more closely.
Confidentiality. NDAs limit how much either side can share before the contract is signed. Client lists are masked. Compensation details are aggregated. Internal documents are summarized rather than disclosed in full. Both sides know this is happening, and both sides know they are making consequential decisions based on incomplete information.
Asymmetry. The acquirer typically has more deal experience, more resources, and more leverage. They have done this before. The selling firm is often doing it once in a career, while still running their business at full speed. They are negotiating with people who do this for a living, advised by lawyers and bankers they hired last month, on a timeline set by someone else.
Intangibles. Financial performance can be modeled. Client concentration can be measured. But the things that determine whether two firms work well together are harder to quantify. How decisions get made. Whether the leadership team trusts each other. What the firm tolerates and what it does not. These show up in conversations, not spreadsheets.
The result is that even rigorous due diligence leaves significant blind spots. According to a 2025 analysis published by the CFA Institute, between 70% and 90% of M&A deals fail to deliver expected value, and inadequate due diligence is consistently cited as a primary driver. McKinsey research finds that 95% of executives describe cultural fit as critical to integration success, while a study reported by MarshBerry found that 75% of people in key roles leave within three years of a merger. The gap between what gets evaluated and what determines success is not small.
What the Acquirer Misses
Most acquiring firms run financial due diligence well. They know how to read a P&L inside and out, audit utilization rates in their sleep, and stress-test a backlog without breaking a sweat. Where the process breaks down is everywhere else.
How decisions actually get made. Org charts describe authority. They do not describe how things actually happen. A firm whose principals make decisions collaboratively in long meetings will not integrate easily with a firm whose CEO makes calls unilaterally and expects them to be carried out. Neither approach is wrong. They are simply incompatible without a transition plan, and that plan is impossible to build if the acquirer doesn’t take this into account.
What the firm tolerates. Every organization has unwritten rules about what is acceptable. Some firms tolerate technical mediocrity if the relationships are strong. Some tolerate weak business development if the technical work is exceptional. Some tolerate neither, and some tolerate both. These tolerances shape who gets promoted, who gets protected, and who quietly leaves. They are typically visible only after months of observation.
Whether the leadership team actually trusts each other. In a small or mid-sized firm, the principals usually present a unified front during diligence. Whether that unity reflects genuine alignment or a temporary cease-fire built around a liquidity event is one of the most important questions in any acquisition, and one of the hardest to answer from the outside.
The client relationships that are actually transferable. Diligence usually examines client concentration and revenue stability. It rarely examines whether the relationship lives with the firm or with a specific person. A client who renews because they trust a senior project manager is a different asset than a client who renews because they trust the firm’s brand and methodology. The first one walks out the door if that PM does. The second one does not. Distinguishing between the two takes more than a contract review.
The hidden dependencies. Every firm has a few people who hold things together in ways that are not obvious until they leave. The longtime office manager who knows where every project file lives. The technical lead who quietly mentors the next generation. The principal whose relationships with regulators smooths permits that would otherwise take twice as long. Diligence rarely identifies these people because their value does not show up in titles or compensation. It shows up only when they are gone.
What the Seller Misses
The other side of the table is rarely written about with much honesty. The selling firm is also conducting due diligence, just with less infrastructure to do it well.
What the acquirer is actually buying. Many sellers assume the acquirer wants what they have built. In some cases, that is true. In others, the acquirer is buying capacity, geography, or a client list, and the culture the seller spent years building is incidental to the deal. Sometimes it is worse than incidental; sometimes it is an obstacle the acquirer plans to dismantle. Sellers who do not press hard on this question during diligence often discover the answer in year two.
Whether the integration plan exists. Does a plan exist, who is running it, and can we talk to people who have been through it with you? All three are questions a seller can legitimately ask. The acquirer’s response, including how readily they make those connections, tells the seller as much as the answers themselves.
What happens after the earnout. Many environmental consulting acquisitions include earnout structures that keep selling principals engaged for two to five years. The terms of the earnout get extensive attention. The question of what happens at year four, when the principal’s financial incentive begins to diminish, gets less. The acquirer is making a long-term bet. The seller, once the earnout closes, may have a very different set of options.
How the acquirer treats people during stress. Every firm looks good during diligence. The acquirer is on their best behavior, and so is the seller. What is much harder to see is how the acquirer treats people when a project goes badly, when a client leaves, when the market turns. This is not something a formal conversation will surface. It shows up in indirect signals: how the acquirer handles friction during the negotiation itself, and what happened to the leadership of firms they previously acquired.
The acquirer’s reputation as an employer. Sellers have few legitimate windows into the acquirer’s culture before signing. Glassdoor, LinkedIn tenure patterns, conversations with former employees, and press coverage of previous acquisitions are usually the best available signals. None of these sources is definitive on its own. Glassdoor reviews skew toward departures, sample sizes can be small, and older reviews may describe leadership teams that no longer exist. But sellers do look at them, and they form opinions. A weak employer reputation rarely kills a deal outright. It does shape how the selling principals feel about the deal they are signing, how confidently they communicate it to their own people, and how quickly the acquired firm’s talent updates their resumes once the news breaks. Employer brand is a strategic asset in M&A whether anyone formally treats it that way or not.
The brand question. If the acquirer’s long-term strategy involves consolidating multiple firms under a single platform brand, the selling firm’s name will eventually disappear. This is especially common in private equity-backed roll-ups, where the platform brand is the asset being built. Sellers who do not understand this going in, or who assume the transition period they were shown will be followed as presented, often find themselves resenting a decision they technically agreed to.
The Things That Cannot Be Learned Before Close
Some questions cannot be answered in due diligence, no matter how well it is run. Confidentiality limits do not allow for the kind of deep, sustained observation that would surface them. This is not a failure of the process. It is a structural feature of how M&A works.
The questions that fall into this category include how the combined firm will handle its first real conflict, whether the acquired firm’s people will actually trust the new leadership, how clients will react when they learn about the deal, what cultural friction will surface in the first six months, and which departures will catch everyone by surprise.
The firms that handle integration well know going in that due diligence cannot answer every question. They go in expecting to keep learning, and they build some kind of intentional process to do it. The specific mechanisms vary. What matters is the posture.
The firms that struggle treat the close as the end of diligence rather than the start of a new phase of it, and the things they could not see beforehand often become the things they cannot fix afterward.
What This Means for the Decisions That Follow
Article One in this series introduced seven decisions that determine whether an acquisition delivers value. Each of those decisions is shaped by what was learned, or not learned, during due diligence.
Brand decisions are easier when both sides surface their assumptions about the name before signing. Talent retention plans are stronger when the acquirer actually understands which people hold the firm together. Client communication works better when the acquirer learns which relationships are transferable and which are not. Organizational structure decisions are cleaner when both sides understand how the other makes decisions before they make them together.
Due diligence is not a phase that ends at close. It is the foundation that determines how steep the integration curve will be. The firms that take it seriously, on both sides of the table, give themselves room to capture the value they paid for. The firms that treat it as a checklist spend the next two years discovering what they missed.
The next article in this series examines the brand decision, what both sides need to bring to that conversation, and how the firms that get it right structure the transition.
References
CFA Institute. (2025). What’s the Winning Ingredient in M&A? The Answer Lies in Due Diligence. Enterprising Investor. February 3, 2025. blogs.cfainstitute.org/investor/2025/02/03/whats-the-winning-ingredient-in-ma-the-answer-lies-in-due-diligence/
Knowledge at Wharton. (2025). Why Many M&A Deals Fail and How to Beat the Odds. Wharton School of the University of Pennsylvania. December 8, 2025. knowledge.wharton.upenn.edu/article/why-many-ma-deals-fail-and-how-to-beat-the-odds/
MarshBerry. (2024). M&A Cultural Due Diligence: Don’t Forget the Culture. marshberry.com/resource/due-diligence-dont-forget-the-culture/
Stambaugh Ness. (2025). Building a Strong Foundation: Employee Retention Strategies for AEC Acquisitions. stambaughness.com.
PSMJ Resources. (2025). Before the Numbers: Why Cultural and Strategic Fit Must Come First in AEC M&A. psmj.com.
