Originally Posted by
mahasamatman
I really think it's all up to the gate agent, as with so many other things. I've only done this once, but they didn't make me pay anything. This was about three years ago, though, so things may have changed.
Might make a difference if you do it in advance or at the gate. If in advance, the phone rep might make pax pay for the higher fare class; if at the gate, the GA might just care if there is a seat in coach or not.