When you decide to buy a used car, You have to pay attention for following factors.

1. Calculate the average mileages per year on the car that you want to buy. usually average mileages per year is between 12,000 to 16,000. any car's average mileages per year is higher than above range.especially German car, German car break point of the mileages are 100,000. This means German car drive 100,000 miles just like a new car.
   
2. The car has high mileages, You have to check the previous owner information. Here is the reason, usually high mileages car was owned by rental company. You can purchase this car with high mileages. If the high mileages car own by individuals. I suggest you don't buy the car.
   
3. Do a real road test drive. Before you make a real road test drive, check the car engine, inside, paint and so on. when you are really driving the car, turn off all the audio and video devices, hear the cars' song. Usually a good condition or fair condition cars' sound are smooth, not too noisy. after you check the sound of the car, drive on the highway for a little bit, if your car comes with cruise control, also check that. when you exit from the highway, push the break, try to feel whether the car shaking or not.If the car shaking that can be several problems on this car. I suggest you don't buy it, the reason is some old car also can be good condition, maybe the owner maintain them very well.
   
4. Purchase from dealers, individuals or auctions, there has no big differences. Important thing is you have to know how to test a used car. Follow above rule, i think you can buy a good car you like.
   
5. Follow above factors, adding your own criteria, for example: gas saver car, or safety, looking, brand. so far.

I believe If you can follow the basic factors of choosing a used car, you can find a good value car for yourself.

If you have any further questions regard to this specific used car selection issue. You are welcome to comment on my hubs. I will try my best to help you.