there are rules for retracting bids
https://www.ebay.co.uk/help/buying/bidding/retracting-bid?id=4013&st=12&pos=1&query=Retracting%20a%2...
When you can retract a bid
You can retract a bid if:
- The seller significantly changed the description of the item
- You accidentally bid the wrong amount. For example, you meant to bid £20, not £200. In this case, enter the price you intended to bid as soon as you've retracted the incorrect bid
- You can't reach the seller. For example, you sent the seller an email and it comes back undeliverable, or you tried calling the seller and the phone number doesn't work
As well as the above, timing is also important when retracting a bid:
- If there are 12 hours or more left before the listing ends, all of your bids can be retracted
- If the listing is ending in less than 12 hours, you can retract your most recent bid if it's been less than an hour since you placed it
Any other bids can't be retracted, but you can still contact the seller to see if they'll agree to cancel a bid for you. Remember, the seller isn’t obligated to cancel a bid so they may not agree.
