If you don't buy the car from an authorized dealer try to find out as many things as possible about the guy who sells the car and the reasons behind this. Another important thing to check is how he got that car and if the papers are complete. If you are suspicious about any of these aspects we recommend to avoid the purchase.
Maybe one of the most important aspects in buying a car is the car history from the manufacturer. These are official papers with every intervention made at the producer's services. You should check there if all the regular maintenance was made on time. If the car doesn't have an official car history at the producer then ask the seller about invoices which can prove the maintenance was made on time at an authorized mechanic.
If you have a friend which is mechanic bring him with you when checking the car, otherwise try to find one. Better pay a mechanic to see the car than having a complete checkout made and paying a lot of money. He should tell you from a few visual checks if the it's worth to go on with the purchase.
If all the above are met then you can schedule a complete inspection of the car at the nearest manufacturer's service. If none is available in the area then try to find the best service in the area. Be careful if the owner is from the area not to take the car at a seller's friend.
Even if the car seems fine take it for a ride, try to feel it, stop the music and try to hear all the suspicious sounds that might come from the vehicle. The best way to test is always in real life conditions.