Sorry to dig up an old thread, but I wanted to add something. In the past I have seen scammers employ long cons in which they join a forum, begin selling items and bide their time until they buy or sell a much larger item in which they scam an unsuspecting forum member.
Their time investment in selling and buying smaller items gives other members a false sense of security. They'll spend 6 months buying and selling sub $100 items, and then buy something much bigger and more $$$.
Money never arrives
The scammed member looks back through the scammers buying/selling history but no alarm bells go off! Everything looks perfectly normal.
By the time the poor member figures he's truly been scammed it's months later and the guy is in the breeze!