Shill bidding is where a 'friend' often the seller themselves, uses another eBay ID to bid on their own auctions to artificially inflate the auction price.

This practice is against ebay rules and can be reported here

(Use: Ask about bidding or buying/problems with sellers/I think a seller is Shill Bidding ....)

Before making a report to eBay, why not take eBays shill bidding tutorial ?

To check an auction where you suspect shill bidding has taken place, simply enter the auction number in the box above and 'click' find.

The result will show you the bidders on that auction, and ALL the other auctions from the same seller, those bidders have placed a bid on !

(Credit to Win Bent for the 'inspiration' of this tool)