How much customer concentration is too much when buying a business?

Build five concentration views

Request:

• At least 36 months of customer-level invoices
• Credits
• Cash receipts
• Gross profit where available
• Contracts
• Backlog
• Accounts receivable

Reconcile total customer data to the general ledger, bank deposits, sales-tax records where relevant, and tax returns. The SBA's buyer guidance includes financial statements, tax returns, contracts, leases, and cash-flow valuation among the materials and methods to evaluate ^[1] .

1. Revenue: each customer's share of annual and trailing-twelve-month sales.
2. Gross profit or contribution: which accounts actually fund overhead and debt service.
3. Cash and receivables: who pays slowly, creates disputes, or dominates working capital.
4. Relationship and contract: seller-owned contacts, renewal dates, termination rights, pricing, consent, and purchase-order dependence.
5. Correlated exposure: common parent, channel, government program, prime contractor, geography, platform, industry, or product.

A top-five table should therefore include:

• More than percentage: years active
• Revenue trend
• Gross margin
• Payment days
• Contract status
• Renewal date
• Termination right
• Price reset
• Decision-maker
• Relationship owner
• Service criticality
• Alternatives
• Known events

Do not invent a universal red line

“Any customer above 10% is bad” and “below 20% is safe” are both shortcuts. A project contractor may naturally have lumpy annual customers. A healthcare provider may have low patient concentration but extreme payer concentration. A franchise may have thousands of customers but one franchisor, platform, or territory dependency. A manufacturer may have a major customer that approved its process and would face high switching costs—or a cancelable blanket order with no volume commitment.

Use bands as internal triage only. For example, a buyer might require expanded work whenever one customer exceeds a chosen share of revenue or contribution, but the decision comes from durability, loss impact, and deal structure. State the chosen trigger and why it fits that business; do not present it as an industry law.

Read the customer history as a bridge

Question	Evidence	Risk signal
Is concentration increasing?	Monthly sales and gross profit by customer for 36+ months	Growth depends on one recent account
Is the account recurring?	Contract, orders, invoice cadence, renewal history	“Recurring” revenue requires repeated discretionary orders
Who owns the relationship?	CRM, emails, meetings, service logs, org chart	Seller is the only commercial or technical contact
Can terms change?	Pricing, termination, volume, assignment, change-of-control clauses	Customer can leave or reprice immediately
Does cash follow revenue?	Receivable aging, disputes, credits, collections	Largest account is also the slowest or most disputed

Illustrative loss-at-close case

Assume a service company has $2.4 million of revenue, $960,000 of gross profit, and $420,000 of normalized EBITDA. Customer A supplies $600,000 of revenue—25%—but $330,000 of gross profit because the work has unusually high margin. Customer A therefore represents 34.4% of gross profit.

If Customer A leaves, the company loses $330,000 of gross profit. Assume only $90,000 of labor and delivery cost can be removed in the first year; overhead reductions take time. EBITDA falls by approximately $240,000, from $420,000 to $180,000. A revenue-only analysis would understate the earnings shock.

Now add structure: the relationship is managed solely by the seller, pricing resets in four months, the agreement is terminable on 30 days' notice, and the buyer's loan payment was sized against the original $420,000. The buyer should underwrite the $180,000 case through the affordability and debt-capacity framework, not merely negotiate a lower multiple.

Verify without damaging the asset

Begin with anonymized data. Assign stable customer codes across invoices, gross-profit reports, receivables, contracts, CRM, and bank receipts. Resolve name changes and related entities. When the deal is advanced and confidentiality permits, propose a controlled verification plan for the most material relationships.

• Seller and buyer agree which customer representatives may be contacted and when.
• The script confirms service, relationship depth, decision process, known changes, and transition—not the buyer's financing or confidential price.
• Required contract consents are separated from courtesy introductions.
• Results are documented consistently and fed back into the risk model.
• If direct contact is impossible, increase reliance on contracts, correspondence, purchase history, backlog, and downside protection.

Match the deal response to the failure mode

Finding	Possible buyer response
Durable account; low transition risk	Proceed, document evidence, monitor after close
Seller-owned relationship	Paid transition, introductions, CRM transfer, non-solicit/noncompete review, retention milestone
Near-term contract renewal or consent	Closing condition, pre-close renewal/consent, or contingent value
High loss severity but uncertain probability	Lower fixed price, holdback, escrow, seller note, or carefully defined earnout
Cash-flow failure in downside case	Reduce leverage/equity exposure, require structural protection, or exit

An earnout is not automatic protection. If the buyer changes pricing, staffing, capacity, or customer service, the seller may dispute the result. A holdback does not replace a contract. Seller financing can align risk but still requires cash to pay. Choose the instrument that responds to the identified failure.

Look past customers

The same method applies to suppliers, employees, referral sources, licenses, locations, digital platforms, equipment, and owners. Ten customers referred by one physician are one referral concentration. Fifty routes dispatched by one manager are key-person concentration. Many marketplace buyers reached through one account can be platform concentration.

Add these dependencies to the due-diligence checklist and the working-capital analysis. Losing a major customer can leave excess inventory and receivables disputes while fixed payroll and debt remain.

Write a concentration decision memo

Before signing the purchase agreement, record the top-one, top-five, and correlated exposures by revenue, contribution, and cash; the contract and relationship evidence; the downside EBITDA and liquidity case; the mitigation owner; and the exact price, financing, covenant, condition, or exit response. That memo prevents a familiar number from becoming an accepted risk without a decision.

Concentration is sometimes the reason a small business is excellent: a trusted specialist can earn strong margins from difficult customers. The buyer's job is to distinguish earned dependence that can transfer from personal dependence that disappears when the seller does.