Online auctions come in many different shapes and sizes, often mimicking real-world auctions in an attempt to draw customers to their websites. The first commercially successful online auction was eBay. While other auction sites have come and gone and some have grown to represent a significant business online, none have come close to matching the success that eBay has seen. The main considerations when looking at online auctions is to ensure that the seller has an excellent feedback record and that the auction site has protective standards in place that will protect not only the seller of the auction item, but the buyer as well.
Community
The community building aspect of eBay, using web 2.0 concepts, has driven the auction site as a model for others to follow. In this type of community, each user gets to rate the transaction, both the seller and the bidder. This way, when you are bidding on an auction, you can see what kind of feedback other users have given the seller. The more positive feedback, the better. Likewise, as a seller, you can see the feedback of those bidding on your auction. With this system in place, it really is a win-win for both the users of the site and the site itself, allowing the users to rate and "police" each other.