Any accessory use on the same lot customary and incidental to any use permitted in this district, such as but not limited to: showroom for the sale of products, provided that no more than ten (10%) percent or one thousand (1,000) square feet, whichever the lesser, of the gross floor area for the entire site is used for retail sales. Such retail sales shall be accessory to a permitted principal use within the facility. Further, such use shall be located on a lot of no less than three (3) acres in size.