New or used your going to have to figure out what your looking at. If you buy used just get the manual to that car and do a complete rebuild. Bearings need to spin freely, make sure you have no broken parts, check the chassis by putting it on a piece of glass. Then go to the track and find some friendly help to make sure everything is good to go. You'll find that at most tracks there's a couple guys who could care less about helping you out but most guys will be eager to drop some knowledge on you.