It's difficult with modern cars. For example, BMWs store the mileage in the gauge cluster, the lighting control module and the keys. If there is a mismatch a "tamper dot" is illuminated in the gauge cluster. Also, the car's information, including mileage, is collected from the key and stored each time the car goes to the dealer. Is it possible to roll back the odometer in a modern bimmer? Yes, buy you need the proper software, and you need all of the keys. But, you can't change the data collected by the dealer.