my 2 cents

once a passenegr tells the GA they are willing to Vol they are put on a list or or immediately told Thanks and have a seat and I will take care of everything once the flight departs

Now IMO once the passengers asks to be put on the list or is accepted if needed then and there eitehr way w/o having discussed what if anything they will get are SOL after the fact

So if the GA hands the person a VDB for $150 its too late for that person to say are U nuts I was expecting $400 at least or to say I just looked at the T&Cs and dont like them.

The time to negoiate was before they told the GA they will be a Vol. If the GA needs them then and there then the GA will remove them then and there from the flight! = I believe they no longer have any Rights to get back onto that Flight and especially into the seat they had reserved

So IMO its the Passenger who needs to know exactly what the GA is offering and what the T&Cs are with Each Carrier, dont come a cryin after the milk has been spilled if you didnt do your homework and ASSUMED something that just may not be the case