^redacted‌I'd do a valuation assuming you had the customer concentration that you'd prefer ("if the customer concentration was exactly what you the buyer wanted to see, what would I pay for this business?" is the question). Once you have that value, you'd then offset customer concentration risks in some way. Lowering the value of the biz upfront might be a tough pill for the seller to swallow but baking in the risks somewhere else in the deal might be easier for the seller to deal with. To reduce risks, have a clause stating if revenues from top X customers drop by Y% over the course of Z years, the seller note gets reduced by some amount. Or, have an amount set aside in escrow that doesn't get paid to the seller if the top customer relationships changes in some way. You could also add in an incentive. If the seller brings in additional customers offsetting concentration risks, increasing revs, etc. they get $ additional in payouts over x years (or something).

Just a few ideas. Sounds like an exciting deal, though. Happy to be helpful if I can. Best of luck!

While not enough to pass on the deal, it is enough of a concentration that it should be factored into the valuation my reducing the multiple. In addition, I'd advise doing due diligence on the customer before close to ensure that they won't take their business elsewhere after the change in ownership.