I had that happen once. I sold an item, buyer never paid. Reported him, waited seven days, got my fees back. Then I relisted the item, and it sold for more than the first time. The 2nd buyer paid, I think I had even shipped out the item when out of the blue, the original buyer pays up. What??? I contacted eBay and they said that since he had not paid and I had gone through all the steps, his transaction was nullified and he had no right to the item.
I refunded his money and never heard from him.