No broker-dealer licensed under this chapter shall effect any transaction in, or induce or attempt to induce the purchase or sale of, any security in this state in contravention of such rules as the commissioner may prescribe designed to promote just and equitable principles of trade, to provide safeguards against unreasonable profits or unreasonable rates of commissions or other charges, and in general to protect investors and the public interest, and to remove impediments to and perfect the mechanism of a free and open market.