Did their payment go through? I would have just not sold the guest the phone if the "problem" had solely to do with their purchase. Seems like a shocker to some that we can choose what we sell, who we sell to, and at what quantity.
If there's one thing a guest has ABSOLUTE NO SAY in, it's whether they can bypass showing you an ID when prompted on the POS. If there's someone who doesn't understand that, I would love to give them a little educating.