I use to be a Store Manager at gamestop, so I have to correct a couple of statements or clarify.
Its $15 for the edge card which give you 10% off used games and an extra 10% on trade ins. It includes a 10 month subscribtion to game informer (the associate always states it takes about 2 months for your subscribtion to kick in. 2 - 12 = 10)
Here's the quoted return policy'
"Used (pre-owned) merchandise and opened new accessories may be returned for a refund within 7 days of purchase or exchanged for the identical item within 30 days of purchase."
So you have 7 days to get a full refund, you have 30 days to reiceve credit. With a reicept of course. If you want credit just return the game after 7 days to a gamestop that doesn't have a copy. Just check online to be sure.