PSN ID
by 
When you are making a purchase at Gamestop.com, on your shopping cart list at the bottom there is an area to put your PowerUp Rewards
/ Edge Cards # OR a Promotional Code. Put this code CAG16 into the promotional code box and click apply, you will now have 16% off all pre-owned games that you are purchasing from Gamestop.com- I have combined my EDGE card discount WITH this code and it still worked!
Here is my proof:
* As you can see, the code does not work on new games such as GT5 on the list, or accessories, such as the steering wheel controller I added to the list. Anyways have fun!!
