Ebay has a policy that if a mistake was made on an offer and purchase, the seller can cancel the sale if the buyer immediately contacts him and pleads his case, e.g., a typo in the offer amount.
Audiogon is not set up to do that. Immediately upon acceptance of the offer, the classified ad is cancelled and fees are applied. No way to reverse it. The seller would have to post a new advert and pay the fees again.