If your eBay auction isn't performing as well as you'd like, you can cancel the auction and all bids on the item as long as the auction has more than 12 hours left. This option is helpful if your item is advertised elsewhere; you may need to cancel the auction if it's sold through another medium. Once your auction has 12 hours or less left, eBay restricts cancellation.
Instructions:
1) Log in to your eBay account. Click on "My eBay," and then click on "Active" underneath the "Sell" tab.
2) Find the auction you want to cancel. Locate the item number next to the auction; either write the number down, or highlight and copy it with your mouse.
3) Access the eBay "End My Listing" form. Use the eBay Help search tool (type "end listing"), or see "Resources," below, to access the form.
4) Enter the item number related to the auction you want to cancel. Click "Continue."
5) Choose "End Listing Early," and then select your reason. Click "Cancel Listing" to cancel your auction.
Tips and Warnings:
If 12 hours or less remains in your auction, you may have trouble canceling it. If there are no bids, you may cancel the auction. If there is a bidder, you can only cancel the auction and sell the item to the current high bidder. Under special circumstances (lost or damaged goods, for example), eBay may work with you. Contact eBay's customer service department for assistance.
Source - eHow
