so I imagine they were only doing it for people who actually mentioned it.

I don't think most people who work for Gamestop give a shit about it. Hell, they even had to send a memo out to all the employees demanding their loyalty. Have you ever had the misfortune of working retail? Ever? I'm sure whoever was helping you was hating the company and FedEX so fucking much that he simply spaced the $5. It happens when you've been screamed at all day about something you had no God-damned control over. People make mistakes, the computer doesn't just magically give $5 off GoW. He also may have been a simple part-timer (these are the ones who make the biggest mistakes because Gamestop only pays them all minimum wage so they care even less about their jobs than the management).