When Commodore got Amigas that were returned as faulty they would repair whatever was faulty (if there was a legitimate problem) and then stamp refurbished on the bottom of the case. Then they would take the Amiga, put it in a new box with new mouse, power supply, books etc. The only thing to distinguish a refurbished model from a new one is the refurbished stamp.
-Edit- Basically everything is new but the motherboard.