How to Avoid Used-Car Disasters

It's every used-car buyer's nightmare: Getting a rebuilt wreck despite doing extensive research.

That's because they're difficult to spot. Even buying a model known for reliability is no guarantee that it won't have problems. That's what Deborah Boulet of Canterbury, Conn., found when she bought a used 2011 Mazda3 and discovered water leaking into its trunk on the day she took delivery. Upon further investigation, her attorney found that the car had been hit by a snowplow and shoddily repaired. Boulet used towels to soak up the water as she fought a legal battle to get the dealership to buy back her car. "I don't trust this car at all anymore, and I drive it as little as possible," she said. "It's been a nightmare."

According to CarFax, a service that provides vehicle history reports, about 20 percent of cars on the road have some sort of accident damage.

Consumer Reports has found that reports from CarFax and its main competitor, AutoCheck, can't catch everything. Differing state laws governing salvage titles allow for loopholes big enough to drive a rebuilt wreck through. Often, even when a car's title is conspicuously labeled as salvaged, consumers such as Boulet never see it. Ask to see the title before you buy a used car, and be especially wary of any car with a "lost" title.

See our list of the best and worst used cars.

Though there is no substitute for hiring your own mechanic to inspect any car you're serious about buying, look for these telltale signs first to thin the herd:

• The close-up: Inspect each body panel for scratches, dents, or rust. Masking-tape marks ­under windowsills or fender edges indicate paintwork.
• Straight and narrow: Uneven panel gaps around the fenders, doors, hood, and trunk can indicate shoddy repair.
• Blend well: Be sure the paint color and finish are uniform, and check inside doorjambs for dull-looking overspray.
• Attractive personality: Run a magnet along doors and fenders. If it doesn't pull toward the car, there may be body filler under the paint, indicating body repairs.
• Crystal clear: Check for moisture fogging in the lights.
• Tread lightly: Make sure the tires have even tread wear. New tires may hide problems.
• Rust bucket: A coating of rust on bolts or hinges inside the doorjamb is a clue that the car may have been submerged.
• Sniff test: A musty, moldy smell in the interior or trunk could indicate water damage.
• Check the tailpipe: Black, greasy residue inside means the engine is burning oil.

For more information, read "How to Avoid a Lemon Car."