I would first set a sell price and ask a 15% diposit before due diligence. If due diligence fails, you keep the diposit, if DD succeeds, you get the remaining 85%.
This is a good test for good faith and allows you to offset bad faith.
This is a good test for good faith and allows you to offset bad faith.
There's a chance that this will drive away a potential acquirer, who may indicate that they are horribly offended by such a request.
That is a good thing. A company offended by the request to put down a slice of the money up front (before they get to see all your private details in diligence!), is likely either just shopping for information, o to be a big pain later in the process. A company who haggles about the deposit but agrees to pay something, likely is a serious buyer with whom you can reach a mutually agreeable outcome.