My guess would be a test program would be wrote to check everything is working. For example you can check the joypad, buttons, keys, touchscreen with an on screen representation, press the buttons and they light up. then do some hardware checks like dead/stuck pixels, speakers, memory, SD check etc. Come to think of it, its not far from my SDL Test program
I reckon it would take a minute or two to perform these tests per pandora so its not that bad as the units would be split up between the stores so this could be possible.