Originally Posted by
joe_miami
True, but that's also true of the whole fare paid. If airlines truly give each other such a deep discount, there'd be an arbitrage opportunity. One assumes airlines are expected to use these reciprocal agreements only when absolutely necessary.
They do give each other that kind of discount, and it is subject to arbitrage, and, in fact, AA was essentially doing exactly that, relying on DL to paper over their lousy operations. DL's response was to request a much higher reimbursement rate from AA, AA refused to sign the contract, and (for a while, anyway), DL and AA reused to transport each others' customers. That's how the "only when absolutely necessary" part is enforced.
BTW: I should walk back at least part of my criticism. I was actually connecting to AUS, which limited my options; it turns out that there was one later UA flight to ORD today than the one I was on, and that flight didn't go out full. So, if the other volunteer was terminating at ORD, or was going to some other destination where there was a later connecting flight out of ORD, then the decision would make sense -- $300 in extra UA funny-money is likely less expensive than buying me a ticket from AA. And if the agent had told me, "Sorry, but I need to wait and see if there's somebody who can make use of the later Chicago flight," I wouldn't have had a problem with it.
Anyway, TL/DR: apparently we don't always have as much leverage as we'd like in VDB situations (although this refusal is still the exception, not the rule).