Well, what I have seen on Ebay is engines that have a lot more gallons or wasn't cared for correctly. One engine was at the 2 gallon mark and was just pinched. Now if you need to pinch a 2 gallon Novarossi, then you definitely don't want that engine. I have personally gotten engines that were supposedly at the gallon or less, and the sleeve were done. Super clean inside, but not broken in or tuned right.
I feel what most are trying to say is, only get a used motor if you know the person or trust them with what they are stating the condition is. It also helps if you have some experience with engines, so if you new to this hobby, you could be opening a can of worms with a used engine and you could spend more money to correct it in the end.