I believe it may have been an MSNBC article that recently offered the hint that one thing to watch for is people who've engaged in a lot of "penny sales." It seems that groups of these people cooperate in offering and buying "really cheap items" from each other so that they can give "buyer's ratings" to each other to run up credibility before baiting the hook for the bigger ones.

That practice apparently is one reason for eBay's limit on number of sales per day(?), and they claim they watch for people who might be doing it; but a gang of thieves can vouch for each other to mislead the innocents.

John