Yes, I could see how that could get hairy; it would also need some ability to rate those giving the feedback, such that if you generate a whole bunch of payments to yourself, those payees don't have reputation on their own, so their review of you as a payer isn't weighted that highly. Then you have that ring-of-trust possibility where Alice thinks Eve is bad, so the fact that Eve thinks Bob is good doesn't impact Alice. But if Carol thinks Eve is good, Carol thinks Bob is good too, so Bob's reputation is different based on who's asking, and 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?