Theres some good advice here. As for burns, I think we've all hit one or two. Easiest way to find out something suspicious is if its the driver or the friend selling the car. If its the driver, get all the info from him/her you can. If its a friend, ask to talk to the driver. If they arent able to be spoken with, walk away. Theirs probably a reason they dont want to talk about this car.