Interesting reading in regard to both eBay and CC. The posts advocating a measured and cautious approach make much sense.
I've bought a few 5%-off certificates for AA flights (around $2.50 to $5.00 a pop). on eBay The code is input into the appropriate field on the AA website, and no problem so far in any way. It's just a promotional code. One seller had something like 10 of these things for sale, and I asked how he had received them. He sent me an e-mail telling me he has a buddy at AA who supplies them for him.
In regard to AA gift cards: With that recent AAdvantage e-shopping promotion and some of the additional %-off deals, we bought $4,400 worth of gift cards for a total credit card outlay of about $3,600. I could see how somebody would do the same and then sell the cards on eBay a bit under face value but still making a net win. Or it could be a shyster. We figured we'll use the cards this year and are getting almost a 20% discount on our travel later on in the year--of course, we won't draw interest on the $3,600 that we have spent in advance.
Like with everything in life, there some people who will treat you right and others who will screw you. I for one am looking forward to access to the CC; I see it as a privilege, and I know that I'll have to earn my respect while being careful at the same time.