It's "buyer-beware" when purchasing a used car, so, be sure to take it to your mechanic for an inspection before handing over any money. If he (or she) finds the vehicle unsafe and/or in need of repairs, determine who will pay for them beforehand and include this in your written purchase agreement.
Check for liens against the vehicle. A lien means that money is owed on the vehicle and although the vendor is in possession of the vehicle, its legal claim belongs to someone else, such as a bank. If you buy a vehicle with a lien against it, you might be held responsible for future payment.