Why not give them a ring first to find out, the Game website lists the varoius branches and contact numbers.
I've not been asked for id when trading in games or taking stuff back that's faulty (always keep the receipts) but I suppose it depends on what you look like as much as anything.
no they dont ask for ID. You can either trade in there and then off something eles in store, or get a gift card with the credit on so you can use it at another time. But beware they are a rip off, they'll offer you about �15 for a new release then sell then on preowned for about a fiver less than the new price.
I tend to use ebay these days as i get more for them.