Originally Posted by carlosdca

In this particular case, what does the phone agent see?
I'm going to guess the agent may see flight oversold, seat to be assigned at airport.
I'm not sure on what basis the agent could have done anything other than voluntary re-ticketing, which is what it seems they were trying to do for the OP and therefore checking aaward inventory.
On a revenue ticket, the agent would have offered change fee + current price ticket, since this is not IRROPS at the point one calls.

In other words, does an oversold cabin give grounds to a free re-routing with an agent on the phone? The standard answer will be "go to the airport".