When you receive returns from a mail art swap, it is considered good form to do the following:
1) Leave an iTrader for the host, thanking him/her for doing the work required by the swap. Further details on this appear in the next FAQ item, "How to Use iTrader."
2) If the swap is a PAT, CAT, or moley swap, you should also leave iTraders for the individuals who created artwork expressly for you.
2) Otherwise, for all standard swaps, leave "reputation" (aka "rep") for the swappers whose cards you received.
To do this, locate the gray bar on the bottom of a particular forum comment (hint: this is the same place you go to reply). To the left of the replying options is a STAR. Click the star, and you can leave a private comment that will also earn the trader reputation points.
Most members prefer rep that is specific ("I am so excited that I received your juggling clown!"), rather than general ("Got your card"), mainly because people like to know where their work ends up.
If you are participating in personal trades or a Monthly Match Game, rather than official hosted swaps, you should leave iTraders, following the rules outlined below.