Play the machine. If you are not able to do that, then look for the behavior of the seller. An honest seller will be upfront about all the issues and freely offer to show you photographs of everything. Look for playfield and cabinet wear. A credit dot would be an easy indicator of an issue with game play. Used games are used and if they don't have issues, they will.....so be prepared to learn and tinker after purchase, even if your game is working perfectly when you get it.