Why not have a "rate a member" kind of system?
"Reputation management."
I believe that this sort of thing has been experimented with in forums (rate the questioners, rate the responders, etc.) It doesn't seem to have caught on much; I think it's too easy to "game" such a system. Eventually you end up with people like politicians, who spend all their time maintaining their reputation, but not actually doing anything 
(For some questions, it's an attempt to get their homework done for them, and a late answer is considered no better than no answer at all. Sigh.)