A lot of the "kiosk people" have more power than you'd expect. Sometimes it's just a matter of finding the one who has bothered to explore the system, or goading them into it.
I looked a little over the shoulder of one of the guys in the AT&T store. They can override pretty much all prices. For example this guy gave me a $39 plan for $19 because they had messed up a previous order. He just typed in different price numbers for each item on the bill. I assume they have a certain amount of discounts they can give away each month.
