if you sell gold, they can easily traqck down your farmers. shutted down 20accounts last week from me in the same second. no connection between them.
i do this as well. the banning likely comes from the selling of gold...and when they check the logs, it's quite evident due to the played time. i still firmly believe that blizzard doesn't care if you are botting...it's how you are botting that they care about it.