I would think that an experienced tech or service manager could tell if they were new or not. After 1200 miles you could very easily have some rust, especially if you have had some rain. New rotors on new cars sometimes have a little rust by the time the car is purchased. The rust should be light though, not caked and flaking. If you are concerned, I would take it back and ask the service manager to have a look at your rotors along with your bill and ask what he thinks.
