When you place a bid or use "Buy It Now", you enter a binding contract.
It is possible for you to cancel a bid you've placed before the end of an auction, but only in the exceptional circumstances listed below. Please note that the number of times you've retracted a bid is displayed in your feedback profile.
It's against eBay rules to withdraw from a purchase after the listing has ended. Learn more about what you can do after the end of the listing.
To cancel a bid, fill in the Bid Retraction form. You’ll be asked to provide a reason why you'd like to cancel your bid. The available reasons are:
Entered wrong amount
Seller changed item description
Cannot contact the seller
Important: Your seller can object to the reason you gave for retracting the bid. For example:
You cancel a bid because you entered the wrong amount, but subsequently don't place another bid with the correct amount. In this case your seller may report that your retraction reason was invalid. We may then take action on your account if we also feel the retraction was invalid.
See Invalid Bid Retraction for more information about what counts as invalid bid retraction and what action we may take.
Note: If you need to cancel a bid quickly because it was placed by someone using your password without your authorisation, please choose "Entered Wrong Amount" as your retraction reason, then let us know about the account theft so we can investigate.
Timing Matters
Up to twelve hours before the end of the listing: All bids you've placed on that item will be automatically cancelled when you submit the form.
During the last twelve hours of the listing: Your most recent bid will be automatically cancelled, as long as you placed it in the last hour. If you want to cancel a bid you placed more than an hour ago, please ask the seller to cancel your bid. eBay can't cancel your bid for you.
hope this helps