If the sale went through, after the offer was accepted, however it was accepted, and the buyer doesn't want it even thought technically they are the buyer, then file a nonpayment claim to recoup your fees.
Since ebay motor sales are non-binding, I'm not sure exactly how this works, or if the rules are different in the UK, but if it shows sold, and the buyer doesn't pay, then you should at least get your final value fees refunded somehow.
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