Remeber that the dealership will actually cut the rotors on the car as were an outside shop cuts them off the car. This means that even though the rotor cuts true off the car it only means its true to the machine it was cut on. Thats why cutting rotors on the car actually cuts them true to the cars hub. This means that once its done there will be no problems. An off the car lathe may cause a shimmy once they are put on the car. Thats why the dealer wants so much.