Can you put a Verizon SIM card into a AT&T IPhone?

I have a AT&T Iphone 4s but there's no SIM card, I'm trying to sell it at gamestop but they need a SIM card in it for temporary use, just to get into the phone and make sure there's no software problems. Both phones are shut off, so it wouldn't be relying on the network just Wi-Fi, would it be able to work?

Nope, it will not work. AT&T and Verizon use different broad bands.