If you have friend or family, and you "give" them a GPU, and they "give" you a nice xmas gift, I would think that UA probably wont take issue with it since they wouldn't know but I suppose you could call that bartering or selling.

Posting an Ad on ebay/craigslist trying to sell it is obvious and you'd just be asking for trouble.

I've never tried it but apparently you can go to the coupon connection and trade your GPU for points, RPUs, etc. I'm not 100% clear on the rules though. I would think that this could be considered "bartering".

Personally, since UA can apparently do whatever they want and take any interpretation they want, I think its best to be cautious and not give UA a reason to target you.