Commodities in liquid form shall be sold only by liquid measure or by weight, and commodities not in liquid form shall be sold only by weight, measure, or by count. However, liquid commodities may be sold by weight and nonliquid commodities may be sold by count only if such methods give accurate information as to the quantity of commodity sold. This section shall not apply to (1) commodities sold for immediate consumption on the premises where sold, (2) vegetables sold by the head or bunch, (3) commodities in containers standardized by a law of this state or by federal law, or (4) commodities in package form when there exists a general consumer usage to express the quantity in some other manner. The director may issue regulations necessary to assure that amounts of commodities sold are determined in accordance with good commercial practice and are so determined and represented as to be accurate and informative to all parties in interest.