Buying / Selling gold -> account action risk

Think I have the equity to sell gold on the side, just curious what the real risk is on getting banned? Not talking massive volumes, but hopefully a few bil a day.

Any guides with info on tactics / expenses involved? Would be super appreciated.

edit: also I assume this isn't the type of income you report?
if it is, what's the legality there with intellectual property?
and if not is it not worth it if you make enough to warrant a possible random audit?