EBay's rule - largely ignored by buyers - is that if a bid is retracted because the wrong amount was entered, a corrected bid must then be placed. Invalid bid retractions are reportable to eBay.
However, as has been said, it's far better to have a bid retraction than a buyer who invents some fault to get a full refund at your expense, with you even having to send a prepaid return label if you want the item back.
If you think this isn't fair, just wait until you sell something valuable. Unfair is when the buyer returns a completely different item, and eBay says that as they never see the item they don't know who has the valid case - but makes you refund the buyer anyway.
EBay has become a very risky place to sell things. A £2 bid retraction barely even registers on the scale of unfairness to sellers.
