Software Deal - Customer Concentration

How have others dealt with extreme customer concentration?

I'm looking at a software business with 2 year contracts and 40% EBITDA margins. Serves a large TAM in a growth market. Sticky product. 25,000 users.

But only 5 (blue-chip multinational) customers and the 3 largest are 70% of the turnover.

Suspect this makes it a non-starter, but I'm curious if anyone has acquired a business with similar concentration successfully (or not). I believe there is an opportunity to markedly improve the underinvested sales & marketing operation.

Vendor is also open to favourable transaction structuring.

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