I once sold a notebook (the scribbling type that you'd keep in your handbag) on eBay. It was a pretty little thing but worth no more than about a fiver tops. Winning bid was £13.50. I was amazed.
I didn't expect the buyer to pay up so I emailed her and explained it wasn't worth that amount. She replied that she'd put in a maximum bid of £13.50, never expecting it to get anywhere near that price, but as she wasn't going to be around at the end of the auction and she didn't want to lose it, she'd put in an 'over the top' bid, but expected to pay a lot less.
I offered her the option to cancel the bid (felt like I was ripping her off) but she insisted she'd pay the price she'd bid. She paid up and left great feedback for me.