Answer:
Fiduciary relationship
Explanation:
The reason is that in a fiduciary relationships, the people mutual understanding of trust and that the agent have to act in the best interest of the principle. So in this case, the broker is an agent of the investor and owes a duty of care to investors and as a result must act in their best interest which means that the agent is not allowed to harm the principle in terms of intentionaly harming the principle by gaining the benefit that the investor doesn't knows.