A colleague of mine told me last month that he was offered to pay at the gate to get upgraded to first. So he paid at the gate and jumped over everybody and got upgraded on his flight MSY to SEA. When he told me that I was confused and didn't quite understand what happened. Now I read this thread and know this is real and happening a lot. Now I know what happened when I didn't get upgraded even though I was at the top of the list and being a G75k and there were F seats hours before departure.