I asked whether i could exchange my 6s i pick up friday morning for a 6s+ at an apple store if by chance they still have one available and got no help at all.
The chat I had online this morning with an Apple rep was downright painful!!! Yes, many have not a whole lot of clue what they are talking about
"Yes, you would be able to. You would just need to pay the difference." How is that no help. Your title should be, "Apple employee understandably doesn't know anything about AT&T stores and their stock levels."
Don't forget the fact that apparently the Apple employee is expected to know AT&T's exchange and return policy (which probably, as an aside, does not provide for exchanges of devices purchased elsewhere...)!
Nobody can guarantee inventory for a new launch product and so nobody will tell you what you can or can't do. That's how launches go. [BTW: This thread is a good reminder for the forum as to what we have in store for the next few weeks. New iPhones = Influx of casual users with oddly unreasonable demands of Apple.]