http://www.carfax.com/car_buying/guide_to_certified_preowned.cfm - More and more people choose to buy certified used cars, as they are cheaper than brand new cars. Take note, not all cars can be certified preowned vehicles. If you see a car for sale by owner, you may want to check if it has been certified. Used cars by owner that are for sale first need to be inspected to see if they can be certified for the extended warranty.