One of my single items was accidentally listed with a quantity of 2. The item sold and I didn't know the other listing was there. This buyer bought the item, I informed him that it was a mistake. He was unreasonable about it demanding that I send his part (that I no longer had) and he wouldn't even agree to cancel the transaction. Then he left negative feedback. I sell used vintage motorcycle parts by the way, so it's not like I can just go order another item and send it to them.