Why not have a test of sorts, like 5 questions that one has to answer before buying from classifieds? For instance, have you done a search on this members name? Have you asked for a member with whom they have sucessfully done business with? Are you using a trusted internet money exchange system such as paypal? Maybe not the best questions, but the idea is to make them atleast read over something that would make them feel a fool to still have been cheated. After all, most of these posts would have been solved by a simple search before hand.