To make changes to your in-store pickup order contact your local store at (xxx) xxx-xxxx. Your order will not be available in the store''s system until the following day. Any changes made to your order will be reflected in the store''s system and will NOT be reflected on the site.
http://www.gamestop.com/gs/help/In_Store_Pickup.aspxPayment
You will be required to remit payment at the store when you pick up the product. Our stores accept Visa, MasterCard, American Express and Discover credit cards. GameStop gift cards, ATM or debit cards are also accepted. If paying by credit or debit card, both the card and the authorized user of the card must be present.
That's not really the best example of "how a CAG operates", that's more of an example of how to be a CAG who constantly gets eye rolls from other CAGs.(1) If they honor a price mistake I can flip for profit, (2) if it is MSRP I will call and cancel, (3) if they won't honor I will file a complaint which usually works if you word your complaint right and make reasonable demands.