More than 60 percent of the cars and trucks on the road are 12 years old or older and the used car business is booming, yet most consumers have little idea what to ask for when selling a vehicle or what to expect to pay for one. Updated twice a year, the consumer edition of the Kelley Blue Book includes the original list price, two retail values (for good and excellent condition) on domestic and imported vehicles, acceptable mileage rates, and more.