The retail sale of farm products on properties where produced shall be permitted, provided that such sales are transacted at a stand or other structure set back at least 40 feet from the front property line and that, in addition to the parking requirements for the applicable zone district, sufficient off-street parking spaces shall be provided to accommodate the maximum number of customers being served and waiting to be served at any one time unless such parking spaces are fully available and permissible on the street immediately abutting and on the same side as the subject premises.