Think of buying a car as a game of poker, the seller is your opponent he may be bluffing he may not, but just as you would at a poker room in a casino you have to try to read the seller like you would in a poker room in a casino.
Always remember to keep your eyes and ears open, when talking to someone about a used car. Make sure to ask lots of questions.
In a casino you are risking your money, in hopes of getting a big return, but when buying a car you just want to get your moneys worth, you want a car that will be reliable and dependable. You do not want a car that wont start on cold days or that stalls until its been running for a half hour.
Make sure to check the undercarriage and under the hood for rust. To a car rust is like cancer. Once rust is found it will spread unless it is cut off and replaced. Under the car and in the engine compartment you will find some rust it is only natural, but you want it to only be surface rust. This means if you take a wire brush to the rusted area you will brush off the rust and get to clean metal.
Next make sure to check the body of the car, for waves and any bubbling in the paint, this would indicate that the car was in an accident or some rust was incorrectly repaired. It is not uncommon for someone selling a car to have rust spots sanded down and painted over to give the car a fresh look, but what will happen is after a month or two the paint will start to bubble as the metal begins to rust again.
Next, look at the motor and mechanical parts under the hood of the car. The engine should be relatively clean from motor oil. If you see large buildups of oil in an area then chances are a head gasket will need to be replaces because of an oil leak.
All electrical and rubber parts should be checked for cracks. Cracks in rubber parts means that the rubber is old and dried out and will probably need to be replaced eventually.
Make sure to ask the owner if he has all the receipts for any work that has been done to the vehicle.
Another important piece of advice is to make sure to take the car for a good test drive. Do not be afraid to drive the car a little hard with the owner with you in the car, chances are they will understand, if they object then maybe there is something with the car they are trying to hide and you should move on to another car.
Many people will tell you that buying a used car is a gamble but if you take a good hard look at each car, and not get impulsive to buy, you can remove any gamble and guarantee yourself a jackpot of a car.