A specialty manufacturer with one customer holding all the profit.
A specialty manufacturer was being sold through a banker, and the marketed numbers looked healthy. In diligence I found what the bank had missed: a single customer was under half of revenue but more than all of the profit. Losing that one account would have turned the business from profitable to loss-making. The customer had no contract and a history of switching suppliers.
The question that surfaced it was not a clever one. It was the question a buyer always asks and a seller almost never does: what happens to the economics if your biggest customer walks away?
By the time that risk was on the table, the only fix, asking the customer to sign a contract, had to happen under the pressure of a live sale, which signals to your most important relationship that you are selling. The deal died. Done a year earlier, on the owner's own schedule, that same conversation is routine, and the business goes to market with the risk already closed instead of exposed.