Clocking involves reducing the mileage of a vehicle by turning back the odometer. It is a common trick used by unscrupulous sellers to obtain a higher price and research shows that on average 1 in 12 vehicles have some sort of discrepancy. The average car does 10,000 to 12,000 miles per year, so if you think the mileage is inconsistent with the age and condition of the car it is worth investigating further.