The Certainty Principle
Edit: It’s makrooh, NOT haram, to sell something when you’re 50%+ sure it’ll be used for haram.
In Islamic finance, permissibility to sell something is tempered by the certainty principle–that is, how certain are you that this thing you’re selling will be used properly?
Say you sell grapes in a specialty grape-only store. A few types of customers come in:
A young woman comes in with her little boy and buys some grapes; you see her feeding him the grapes as soon as the cashier scans it through.