You shouldnt get banned tbh. My friends and I have bought and sold gold for awhile now and none of us have ever been banned. Just wouldnt do it on a newly created account tbh.
Buyers should honestly have no worries about buying gold. Think about drug-dealers; is law enforcement looking to arrest the people using the product, or the people supplying it?
I've purchased on an account multiple times from the same supplier and never had an issue. There is a small chance you can be banned, but generally the risk is falling on the sellers and the mules that they use to handle the gold.
Just be sure to trade random items. Although it's nothing more than superstition, I'd say it certainly helps. But as everyone else has said: non-existent. You won't be banned