It's just like a junkyard. They buy wrecked/broken
cars and sell them for parts or scrap metal.
In the auto junkyard world there's the concept of "salvage title" for motor
vehicles and the whole process is nicely codified by the state.
In the military surplus world there's the concept of "de-milling" surplus
but I'd be surprised if that applied to a pile of Macs.
Tim.