I was looking at an item on eBay, on my iPhone.
Going to press "Watch this item" I hit "Buy it Now", it took me to the confirmation page and I thought sod it I may as well have it, so pressed confirm.

Now the issue is twofold- number one I am an idiot, and it is the wrong part.
Number two I contacted the seller and explained that it was a mistake, and could I possibly retract the bid, sorry for the inconvenience etc.

He says fine, but wants a fiver for wasting his time, fees etc.

The item price was £20 (with postage of £4, but I'd have picked it up).

Now I have never sold anything through ebay- will relisting it cost him £5?

What would the lfgss community call a fair price in this situation?