I've been reading with interest all these posts about the stealing of upgrades, particularly the part about airlines letting someone stay in biz/first, then charging their credit card for the difference in price. Now, I'm not advocating the theft of these seats, but if someone did this and they challenged the additional charges on their credit card, how could the airlines prove that the charge was justified? Wouldn't the thief have his boarding pass to "prove" what he should have been paying for? It seems like someone could contest and overturn such a charge pretty easily. Just wondering...