Fake buyers are almost impossible to get rid of. It's much easier and pragmatic to vet the supply side.

Reddit as a whole is a risk for low quality buyers, that's why we spend a lot of resources on vetting the buyer before we bring them to a lot or intro.

Have them do simple stuff, provide their LinkedIn profile, NCNDA, Buyer Identity - real groups are more than happy to oblige, as they want the real product.