Those are usable IN-STORE ONLY. NOT VALID TOWARDS DOWNLOADBLE CONTENT, GIFT CARDS, RESERVATIONS, OR POSA CARDS.TWO CERTIFICATES OF THE SAME DENOMINATION CAN NOT BE USED IN SAME TRANSACTION. EXPIRES 12/31/15

That's all you need to know. I will send them as .pdfs, because that's how Gamestop hands them out. I've been collecting a bunch of those, since my friends are too lazy to go to the store and order everything online, so I just bought the certs in bulk.
I'm new here so I'll be going first. I'm looking for like a 25-50% rate, denominations are 5,10,15,25 and 50 dollars.