Buying a used car -- either privately or from a dealer -- is a gamble. But there are some things you can do to tip the odds in your favor.

If you're lucky, you can buy a used car with a known history -- from a relative, friend or neighbor. Be more wary with other private sellers.

Ask about the car's condition and mileage, and see if the seller will let you look at repair bills. At a minimum, see if the service sticker on the door jamb shows that the car has been maintained diligently.

Carefully inspect any used car you're interested in. Bring along a friend to help -- and do it on a clear day. Rain, darkness or the glare of a car lot's lights can hide some telltale signs of trouble.

Dark stains on the pavement under the car may mean leaks. Wet, oily stains on the underside of the engine or transmission signal trouble. Greenish-white stains on the radiator may indicate pinholes. Check under the hood for leaks or excess oiliness around hoses, the valve-cover gaskets, the master brake cylinder and other engine components.

If you see fresh welds on the frame, fresh undercoating on an older car, or fresh paint on a car less than 3 years old, it may have been in an accident.

Look for rust, especially in wheel wells and rocker panels below doors. Push down hard on each fender. If the car rebounds more than once, it may need new shock absorbers. Check tires, including spares, for uneven wear. Worn-away treads on a "low-mileage" car suggest odometer tampering.

If the front wheels move or clunk when pushed or pulled at the top, the suspension joints or bearings may be badly worn. Try all the hardware and controls to be sure they work. And look carefully at rubber pedal covers. On a low-mileage car, they shouldn't be worn heavily, nor should they be brand new.

Once the car has passed the preliminary inspection, test drive it over a variety of roadways. Ask a friend to help. The car should start easily and accelerate smoothly. Steering should be smooth and precise without too much free play or vibration over a variety of roadways. Drive along a deserted road at 45 mph, and brake fairly hard but don't lock the wheels. The car should stop quickly without veering. The brakes should not vibrate or grab.

Have your friend watch from behind. Then, drive straight ahead through a puddle, if possible, to see if front and rear wheels move in line. If they're not exactly in line, the car's frame has probably been bent in an accident.

Drive at highway speed. Lift your foot off the accelerator for a few seconds, then press down hard. Have your friend watch the exhaust smoke. Blue smoke generally means burning oil. Billowy white smoke, particularly in warm weather, may indicate water in the combustion chamber. Black smoke usually means just a carburetor adjustment.

Drive on a bumpy road at 30 to 40 mph. If the car steers poorly, bounds, leaps, squeaks or rattles, the suspension may need attention. Stop, get out and kneel beside the car as it idles. Sputtering sounds from underneath indicate leaks in the muffler, the exhaust pipes or the manifold.

Finally, if the car still looks good, take the car to a qualified mechanic or diagnostic center for a professional opinion. If repairs are needed, get a written estimate. The seller may lower the price or pay for the repairs.