A single customer representing >30% of revenue can destroy value. Or it can anchor long-term stability. The difference lies in contract quality, switching cost, and margin profile. It is rarely the number itself that matters.
Customer concentration is one of the first things a buyer notices in due diligence, if not before. It gets flagged, sometimes dramatically, and deals have collapsed on the back of it. But the instinct to treat it as an automatic red flag is too blunt. The real question is what sits behind the number.
The risk is real — but it is specific
If a business derives 35% of its revenue from a single counterparty, on a rolling 30-day contract, with no meaningful switching cost on either side, that is a problem. Not because of the concentration per se, but because the commercial relationship is fragile. The customer can leave. Quickly. And the business has no structural protection if they do.
The same concentration looks very different in a business supplying a critical component under a three-year exclusive supply agreement, where retooling costs and qualification lead times make switching genuinely expensive for the buyer. Here, the concentration is a feature, not a fault. The large customer is effectively locked in. The revenue is predictable. And the margin is likely strong, because the seller has pricing power within the relationship.
This distinction matters enormously in how you value the business and how you structure a deal.
What to look for before forming a view
There are three things that determine whether concentration is defensible: the contractual framework, the switching cost, and the margin profile.
On contracts, the key questions are duration, notice periods, renewal mechanics, and whether pricing is fixed or subject to annual renegotiation. A multi-year agreement with automatic renewal and no unilateral break clause is worth a great deal more than a letter of intent or a preferred supplier status that exists in practice but not on paper. Many SMEs run large relationships informally. That is a structural weakness, regardless of how long the relationship has been in place.
Switching cost is harder to assess but equally important. If the buyer’s operations genuinely depend on your product, your certifications, your tooling or your institutional knowledge, then switching is expensive and disruptive for them. That dependence is a form of protection. If, on the other hand, your service is broadly available and the only reason they stay is habit or relationship, then the revenue is more exposed than the longevity suggests.
Margin profile is the third lens. A concentrated customer generating above-average margin is a fundamentally different proposition from one that accounts for 30% of revenue but is price-sensitive, demanding, and operating on thin terms. Volume without quality of earnings is not the same as value.1Margin profile is the third lens. A concentrated customer generating above-average margin is a fundamentally different proposition from one that accounts for 30% of revenue but is price-sensitive, demanding, and operating on thin terms. Volume without quality of earnings is not the same as value.2Margin profile is the third lens. A concentrated customer generating above-average margin is a fundamentally different proposition from one that accounts for 30% of revenue but is price-sensitive, demanding, and operating on thin terms. Volume without quality of earnings is not the same as value.1Margin profile is the third lens. A concentrated customer generating above-average margin is a fundamentally different proposition from one that accounts for 30% of revenue but is price-sensitive, demanding, and operating on thin terms. Volume without quality of earnings is not the same as value. (For more on Quality of Earnings see our earlier post here: https://mercury-finance.co.uk/why_quality_of_earnings_matters/ )
Concentration does not have to be a no-deal
Plenty of very good businesses have been acquired with significant customer concentration, and plenty of those transactions have created real value for buyers. The mistake is to let the headline number drive the outcome rather than the underlying risk assessment.
What concentration does require is honest pricing and intelligent deal structure. If the risk is real, it needs to be reflected somewhere. That somewhere is not always in the headline multiple. Sometimes it is better expressed in how consideration is timed and tied.
Earn-out mechanisms are the obvious tool, but they need to be designed carefully. Linking deferred consideration to the retention and performance of the concentrated customer aligns the seller’s incentive with the risk the buyer is absorbing. If the customer stays and performs, the seller earns the upside. If they leave, the buyer has not overpaid for a business that no longer exists in the form they acquired it.
Escrow arrangements serve a similar function. A portion of consideration held back, released on the satisfaction of defined conditions around customer retention, provides a structural buffer without necessarily reducing the total price. For a seller confident in their customer relationships, this should be acceptable. For a buyer nervous about the concentration, it is essential.
The point is that matching the timing and amount of consideration to the actual transfer of commercial risk is not punitive. It is rational. It is how a deal reflects reality rather than optimism.
A word on the downside case
Any analysis of a concentrated business needs to model what happens if the large customer leaves. Not as a theoretical exercise, but as a genuine scenario. How long does the business survive on its remaining revenue base? What cost structure can be adapted, and how quickly? Is there a realistic path to replacing the volume, or does the business structurally depend on that customer to function?
In some cases, the answer reveals that the business is viable without the customer, just smaller and less profitable. That changes the valuation but does not eliminate the opportunity. In other cases, the analysis shows that customer departure is effectively terminal. That changes the conversation entirely, and the deal structure must reflect it. Maybe a majority of consideration needs to be deferred. Maybe the upfront payment needs to be sized around the floor value of the business without the customer, with earn-out covering everything above it.
These are uncomfortable conversations to have, but they are necessary ones. A seller who refuses to engage with the downside scenario is either not being honest or does not understand their own business.
The bottom line
Customer concentration is a risk factor, not a disqualifier. The businesses worth buying with concentrated revenue are those where the concentration is contractually protected, structurally defensible, and commercially profitable. The deals worth doing are those where the structure honestly reflects the risk: where the buyer does not carry alone what should be shared, and where the seller is rewarded for what actually transfers, not just for what existed on the day of signing.
Get that alignment right, and concentration stops being a problem. It becomes a negotiation.
Mercury Finance provides corporate finance advisory for business owners, investors and executives navigating transactions. If you are considering an acquisition or preparing a business for sale, we are happy to discuss how concentration and other value drivers should be assessed and structured.
More on business valuation on http://icaew.com