“Foreign commerce grain business” is defined as the business of buying grain for sale in foreign commerce or the business of handling, weighing, or transporting grain for sale in foreign commerce. This provision shall not include:

(a) Any person who only incidentally or occasionally buys for sale, or handles, weighs, or transports grain for sale and is not engaged in the regular business of buying grain for sale, or handling, weighing, or transporting grain for sale;

(b) Any producer of grain who only incidentally or occasionally sells or transports grain which the producer has purchased;

(c) Any person who transports grain for hire and does not own a financial interest in such grain; or

(d) Any person who buys grain for feeding or processing and not for the purpose of reselling and only incidentally or occasionally sells such grain as grain.