Paragraphs are your friend.
Take a step back. You engaged an auctioneer to find someone to buy your house. The auctioneer found someone who paid a booking deposit. These deposits are refundable as the purchaser can pull out until the contracts are signed.
You have decided that you do not want to sell your house, the auctioneer has fulfilled his side of the agreement and is entitled to raise a fee and have it paid.