A few simple prepurchase steps can put the brakes on a crime that costs used-car buyers about a billion dollars each year: odometer fraud.

Odometer fraud is the illegal practice of rolling back odometers to make it appear that vehicles have lower mileage than they actually do. The National Highway Traffic Safety Administration reports that about 452,000 reported cases occur every year and the average odometer rollback takes 35,000 to 40,000 miles off of a vehicle-boosting its price by about $2,500.

Here's how it affects consumers: Imagine buying a three-year-old car with an odometer rolled back from 80,000 miles to 30,000 miles. Most likely, you would pay top dollar for the vehicle, assuming that because it has so few miles, it is in prime condition, will provide you maintenance-free use and still retain some resale value down the road. However, because of the actual mileage, the car is likely to experience breakdowns and need potentially costly repairs.

Try these tips for spotting odometer fraud-especially if the car you are considering has a digital odometer. Digital odometers may actually be easier to roll back than traditional ones.

? Check the tires and maintenance records. Be certain the odometer mileage matches up with the oil change records. Also, if the odometer shows less than 20,000 miles, the car should still have its original tires.

? Look for wear and tear. Does the wear on the brake pedal seem consistent with the odometer reading? What kind of shape is the interior of the car in? (Look for worn floor mats, upholstery, etc.) Does the car drive like a new car or one with many miles on it?

? Track history through the vehicle identification number (VIN) and title documents. The VIN is a 17-character code found on the dash and title of every car in the U.S. Use it to run a search with a company such as Carfax, which offers reports on vehicle history and mileage. In addition to helping people spot odometer fraud, the reports can reveal whether the car has been in an accident, if it's been damaged by a flood or whether the vehicle has been used commercially as a taxi or rental car.

The company's database contains information gathered from nearly 8,000 sources in the U.S. and Canada.