They are what are known as "fiduciary" duties, and they're enforced by the local state bar association acting on complaints and malpractice lawsuits by aggrieved clients.
So, say I came to lawyer, he gave me wrong advice off the record, because wanted me bring him profit, then charged me $20k for 'legal research' with subsequent heavy litigation, what bar will do?
It is nice that there are bars, but do they make any difference?