The gold sellers don’t care if you get banned, they will play it as a minor inconvenience or something, they’ll already have your money and no bliz rep is going to hunt it down for you.
The fact that bliz could be using AI algorithms that track the movement of gold kind of says its a matter of when not if you get banned for gold buying.
But like I said; Ferengi Rule of Acquisition #1 Once you have their money, you never give it back.