eBay is a gigantic online flea market, and just like meatspace flea markets, it has plenty of scams. Many claim that eBay does little to curb many of these, because it profits from them.
- Shills: One of the easiest ways to drive up the value of an item you are selling is to create a second account and make small bids on your own items. If you accidentally win the item, you can always offer it outside of ebay to the highest bidder, or claim that the high bidder was a no-pay, and relist the item for free.
- The fake dutch auction: If you have a large number of an item to sell, only post one of them. Then, use a second account to drive up the value of the item, and just before the auction ends, snipe the auction with this account. After the auction has closed, contact each of the bidders outside of Ebay, offering them the item at their highest bid. If you play this right, they will be infuriated about being sniped, and will buy at the highest price. Meanwhile, you pay to list and sell only one of the items. If you still have some items left, claim that your sniper account didn't pay up, and re-list the item for free.
- Bid Shielding: A buyer's scam. Find a newly-posted item you want with a low current price and no reserve. Place an excessive bid, like ten times the value. Then, with a second account, immediately make another bid just slightly under your excessive bid. This drives the current bid up to your excessive bid, and nobody will bid over you. Then, with 15 seconds left in the auction, withdraw your second bid. Your excessive bid drops back to the initial price, and you win the auction at that opening price. This scam is highly visible, but difficult to prove. On the other hand, despite Ebay's statements to the contrary, you won't recieve any negative feedback.
- Shipping and handling: Sell something (whether fairly or not) and charge extra for shipping and handling. How do you think so many people are making money on laser pointers?
- Informational CDs: Buy a cd burner, collect some legal garbage like shareware, the Anarchist's Cookbook, or lists of government auction houses. Offer them on Ebay in huge dutch auctions (you can always burn more CDs) for $1.99 each. There are always suckers that will bid on these, as long as you include enough dancing hampters and midi songs on the bid pages.
Note: I don't condone doing any of these. In fact, I'd prefer that you didn't. I've been hit by the fake dutch auction far too often, and it makes buying things legitimately much more difficult.