it's the responsibility of the individual members to maintain their own good/bad user lists. Would you think that's a good thing or a bad thing to give the individual players that level of control/responsibility?

If it's explicit, I think it's a non starter and nobody will bother with it, especially not just for instant payments.

If it's just a case of "link your wallet with your Facebook account" and requires no more effort than that, some people might, but of course the user experience would be rather random. Hey why did that guy in front of me get instant payments and I had to confirm even though we bought the same things?

I'm not a big fan of UX's that appear totally random to the user.