Rules that must be followed by financial advisors when selling investments to the public, which say that brokers have to make certain that the investments they sell are suitable to the buyer. For instance, an 80-year old retiree shouldnÂ’t be sold a risky stock; Treasury securities would be more suitable for this person. If suitability rules are not followed and the investment loses money, then the broker and his firm may be liable to the investor for damages.