Buying used is a risk. If you know the owner and have seen the engine run more than once and fly on a plane then it probably is safe to buy. I bought a plane with an engine. I have to run it with the high speed needle almost all the in and the low end is picky. It probably needs to be clean and have a piece of dirt in the high speed. Cleaning it would probably be good. I didnt have much money for a second plane and i snatched up the plane when i saw it. It flies well but a new engine would have been nicer. Just remember it is a risk, consider how much work may need to be put into it and it may not run right.