Common sense rules no matter whether you are trading or buying outright.

1. New trader/seller = no medium or large purchases unless you pick them up in person
2. Seller with a number of positive feedbacks = ok to buy/trade higher dollar item
3. Seller with only a few or no feedbacks, but you recognize as active on the boards = ok to buy/trade moderate items

There is no way to totally protect yourself, so just use the common sense approach. If someone is offering a deal thats too good to be true then it probably is. If its a pretty good deal and no one else shows any interest, then either its an item that only appeals to a few or there is something about the seller that is making people be cautious.

My personal rules are that for any item over $100, I want the seller to send their real name, phone number, and physical address via e-mail.

Duke