A stated or implied requirement by a regulatory body that a broker or investment adviser must reasonably believe that a certain investment decision will benefit a client before making a recommendation to him/her. That is, the broker or investment adviser must act in good faith, and may not knowingly recommend bad investments. Different regulators and self-regulating organizations incorporate suitable rules in different places in their bylaws. Two commonly referenced suitability rules are Rule 2310 for the Financial Industry Regulatory Authority and Rule 405 for the NYSE. See also: Due diligence, Prudent-person rule, Twisting.
A National Association of Securities Dealers guideline that requires a brokerage firm to have reasonable grounds for believing a recommendation fits the investment needs of a client. See also Rule 405.