The topic heading is somewhat misleading - it should be modified to reflect that the seller was caught selling American miles. As will be discussed below, most other airlines are not as ruthless as American in pursuing people who sell miles and upgrades.

On average, about 50 Southwest coupons are auctioned on ebay every day. To my knowledge, Southwest does not pursue these people because it has determined that it is better for business not to annoy its best customers.

In addition, there are dozens of ebay auctions each week for upgrade coupons from United, Northwest, Continental and other airlines. Although these certificates cannot - by their terms - be sold for cash, the airlines have apparently decided that it is not worth the trouble to pursue the sellers (no doubt very good customers if they have upgrades to spare).

American Airlines is the exception to the laissez fare rule. I once tried to sell an AA discount certificate (not miles) that I received in the mail through a VISA promotion. Within 1 day, ebay had shut down my auction as a violation of its rules. American apparently believes it is a good use of personnel to monitor ebay for such auctions, and ebay management (who are generally wimpy about such things) has agreed to pull auctions for American. I think that United also monitors mileage auctions but don't have any first-hand experience.

It is not difficult for American to figure out who is selling miles, as ebay has account information for all sellers and apparently is willing to violate your privacy by providing it to American.

So the moral of the story is: Don't sell miles on ebay and don't sell anything that relates to American Airlines.