(7) The prohibition against the offering of unwrapped food samples to the general public unless the offering and acceptance of the samples are continuously supervised by an agent of the entity preparing or offering the samples or by an agent of the entity on whose premises the samples are made available. As used in this subdivision, "food samples" means unwrapped food prepared and made available for sampling by and without charge to the general public for the purpose of promoting the food made available for sampling. This subdivision does not apply to unwrapped food prepared and offered in buffet, cafeteria, or other style in exchange for payment by the general public or by the person or entity arranging for the preparation and offering of such unwrapped food. This subdivision shall not apply to open air produce markets nor to farmer market facilities operated on land owned or leased by the State of North Carolina or any local government. The rules shall contain a system for grading establishments, such as Grade A, Grade B, and Grade C. The rules shall be written in a manner that promotes consistency in both the interpretation and application of the grading system.