Always check for cracks, usually around welds. Make sure it's the right size for you. If it isn't, wait. Take it for a test ride, make sure the suspension works., ideally it should be serviced if it can't been. Chains are usually worn, so expect to potentially replace it. Make sure the brakes work well. Make sure there is no slop in any bearings... How old is the chain? Doesn't looks terrible, tough to say without seeing in person.