If you look carefully through the wheels, you should be able to see at least a portion of the pad. If you remember what the old pad's thickness looked like, it will be very obvious if they are new pads. I highly doubt the shop would keep old pads laying around for a few days and then put them back on your car.
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record