Originally Posted by
appleguru
Has worked ok for me (so far?) for complimentary upgrades... IE, called, agent quoted an infant price that was more than 10% of our C- fare. When asked to explain, he indicated it was based on the C+ fare, as that was the cabin we were currently seated in. Asked him to downgrade us, reprice, issue, and then upgrade us again, which he did; new quote was the expected 10% and we ended up back in C+... But good to know it doesn't work for paid upgrades; that makes sense.
I think this is YMMV territory. I’ve clearly remember having to pay 10% of the difference between fare class booked and fare class upgraded to at the gate, and also remember it getting a little hairy in terms of how much time it took for them to sort it out.