on 04-01-2013 07:13 PM
If you are the seller http://offer.ebay.com/ws/eBayISAPI.dll?CancelBidSh
If you are a bidder, you promised to keep your bid on that auction until it ended absent specific extraordinary circumstances (and to pay for it if you won). If you think you have such extraordinary circumstances, you can either describe them to us with specificity (including when you bid, when the auction ends, and why you changed your mind) and we may be able to suggest one or more solutions to your problem. Or you can beg the seller to cancel your bid, but s/he is not required to do so nor to acknowledge your request.
on 04-01-2013 07:12 PM
Cancel: Only the seller can cancel a bid. Contact the seller and explain. The seller may cancel, as the seller is not required to. Ask nicely.
Retraction: A bidder can only retract under certain instances, like making a typo and entering the wrong amount. Like entering $500.00 instead of $50.00. You can retract the wrong ($500.00) amount, but must instantly re-enter the correct ($50.00) amount.
on 04-01-2013 10:44 PM
This link explains bid retractions-