I don't believe airlines will always oversell by another seat if someone is willing to pay full fare.

Assuming a web site is the same as phone or at the airport in person, there are lots of flights for which you cannot buy a ticket, no matter what.

I read about a man who wanted to take an AS flight to see his daughter in the hospital before she died. He was at the airport, begging for a seat (presumably full fare), and AS couldn't find volunteers. They could have added another seat to inventory, handed him a ticket, and involuntarily bumped someone from the flight, but they didn't.

[This message has been edited by JS (edited 06-13-2002).]