Originally Posted by Gongzuokuang

I actually just called United and was told it would be no problem for me to pay.

I had read some threads on this board that suggested the carrier might ask that the credit card that paid for the ticket be presented... which was my "denied boarding" concern.

United said NO, once ticketed it is no problem. Only issue might be the pax wanted to upgrade using the same card, or charge baggage, or something like that.