Having not participated in the Kellogg's promo myself, I'm curious as to what exact merchandise was being sold in that Ebay auction. Were the certificates being sold something that was printed by AA and inserted by Kellogg's into the snack boxes? Or is the "coupon" part of the actual snack box itself? If you're selling coupons, the airline has every legal right to bust you if they can - voiding your AAdvantage account as punishment. If you are buying/selling the actual Kellogg's product or Kellogg's packaging, then AA probably would have less grounds to punish you. Having said that, the airlines usually win these battles, and it's not worth the hassle anyway.

As a side topic: who in their right mind would pay $65 for 2000 miles anyway? There are dozens of other (unquestionably legal) sources of AAdvantage miles at a far better rate than 3+ cents/mile.