Watch for shills and shields. Spotting a shill on the Internet can be difficult, but it's not impossible. Do a search of a seller's past sales. Often the same shill will have bid on everything the seller has offered, to artificially jack up the price of the seller's offerings. To spot a shield, look for the same person in other auctions in which the winning bidder has participated.
Some sites allow sellers to cancel suspected shield bids.
Contact the other party by phone. Buyers usually pay the shipping and insurance costs. Choose a safe payment and shipping method. Buyers should pay in a way that can be traced, such as with a credit card or check. Since the buyer has to sign for the package, she can't say she never got it.