We should have something like Reddit, a trust system.
-Person A and Person B want to trade.
-Person A and Person B both send their trade details to a moderator.
-Person A and Person B ship items.
-If both people are satisfied and got what they traded for, a moderator will put a symbol somewhere, like under their post number, that will show they are trustworthy.
-If the deal does not go as intended, the person who messed it up will receive a ban.