Over the years, I've heard more than one story of a would-be flyer showing up at a check-in counter, asked to wait and in a chat with a suited person or two, told they could fly if they purchased an available (current, walk-up) fare.
I'd never risk that, myself, and figure if I left someone out there holding the bag with miles or points I sold a broker, my karma would be the mother of all IRROPS and airline foul-ups.
