I agree on airline upgrades: I can't imagine an airline handing out int'l upgrades worth thousands of dollars to everyone showing up with a strange-looking ID card. If there's excess capacity up front, they are going to find their highest elites in coach and move them up before giving a "referral agent" the UG. In fact, I would imagine that most airlines would rather fly the seat empty before giving it to someone with such a card.

For Hilton hotels, you can view the Travel Agent rates online. They are usually the same as - or a little lower than - the AAA rates. I'm going to guess that Marriott and Starwood are similar, although I've never researched it. Also: those 50% off UA or AA coupons will get you down around the AAA rate as well (which is usually roughly half of rack rate to begin with).

Car rental rates are a crapshoot. If you look hard enough, you can find a good rate on your own. A bogus travel agent card won't provide you magical results at the rental counter. Rental car employees barely know the rules for their *own* rates/programs, let alone someone else's.

Bottom line: Don't buy one of these worthless cards on Ebay. AAA seems to be a good avenue to hotel (and maybe rental car???) discounts, and you even get other benefits as well. Most importantly: everybody recognizes AAA as 100% legit. (BTW, I'm not a AAA member.)