We want to mention right off the bat that the vast majority of sellers and buyers at online auctions are honest people, and deliver on their promises. According to eBay, only one auction in 40,000 on their site ends with a reported case of confirmed fraud. That doesn't take into account unreported cases, and it's little comfort if you're the one in 40,000. Almost 500 reports per week. And the fraud isn't solely committed by the sellers.
Buyers can be just as sneaky.
The most important thing is to learn the ropes. If we had to offer you just one piece of advice about buying and selling on online auctions, it would be to always carefully check the feedback on the seller you're considering buying from. We don't ever buy from a seller who doesn't have at least 10 positive reviews. If you're the seller, check out the buyer's feedback as well. If you are really concerned, consider using an escrow service.