I think it would be a good idea to have a system where users can rate each other overall, like kindness/trustworthy/helpful/etc/etc.
Have a little area where it would show stars or some icon as to how good their reputation is.
But limit the option to review other users to those who have been here a while or have a decent amount of posts(to help prevent multi's boosting someones rep)
Quote
Example:
User:SomeRandomRudeGuy
Total: [+][+][-][ ][ ]
Helpfulness [+][+][+][ ][ ]
Trustworhyness [+][+][-][ ][ ]
Personality [+][ ][ ][ ][ ]
Overall [+][+][-][ ][ ]
Helpfulness [+][+][+][+][ ]
Trustworthyness [+][+][+][ ][ ]
Personality [+][ ][ ][ ][ ]
Comment: "I successfully traded such and such with this person and would consider trading with him/her again. Though I must say rather impatient and kinda rude."
Overall [+][+][ ][ ][ ]
helpfulness [+][+][ ][ ][ ]
Trustworthyness [+][+][ ][ ][ ]
Personality [+][ ][ ][ ][ ]
Comment: "This guy was kind of an ass, however the trade was successful. And his rudeness wasn't very helpful for the transaction."
Let me know your thoughts!