Apparently AA gifts CK to big spending companies who, in turn, can gift the status (in this case a challenge) to whomever they want - with the intent being a frequent flyer in the company who will continue to spend $$ on AA. I'm pretty sure, however, that outright selling it ala eBay is not permitted....
How would you be sure? I'm absolutely sure you have no first or second-hand experience of how this works. From what basis are you "sure"?