I have a big marketplace with lots of game trades. What do you think about a feedback system?
For every trade in the marketplace section of a forum a user can give a positive or negative feedback and the total amount of negative and positive feedback is shown under the user avatars ...

The same type of system has been proposed here already.

Some have used the creation of personalized profiles to create a reputation type feature. You might be able to implement that type of thing on your board, to achieve what you are looking for.

Skittles