Few purchases are more problematic than that of a used car.  The transaction is fraught with potential pitfalls, and the unsuspecting consumer can easily make any number of costly mistakes in judgment.  

The best way to protect yourself is to do your homework.  Check every web site, magazine, and information source regarding the vehicle you're planning to buy.  Learn it inside and out.  It will help you when you're giving the car the necessary once over.  

When inspecting the vehicle, give the frame a close look, making certain all the body parts line up, the doors work properly, and the paint matches.  Don't forget to check the tires.  Kicking them may seem cliché, but checking them for wear is a must.

Check under the hood.  Look for any loose hoses, worn belts, or other obvious flaws.  Also inspect the various engine fluids.  The oil shouldn't smell burned.  The transmission fluid should be reddish, and the radiator water should be tinted slightly yellow or green.  

Once inside the car, turn the key and check to see if all the warning lights and gauges are in proper working condition.  Rev the engine and listen for any knocks or unnecessary racket.  Smoke is certainly a red flag.  

Always take the car for a test drive.  The steering should be true, and the shifting of gears should be smooth and easy.  The steering wheel should never rattle at higher speeds.  Cornering should be precise.  And pay extra attention to the brakes.  Any screeching, whistling, or grating could be a sign of trouble.