In determining whether a sale or service is recognized as a retail sale or service in a particular industry, there are available to the Secretary a number of sources of information to aid him in arriving at a conclusion. These sources include: (a) The legislative history of the Act as originally enacted in 1938 and the legislative history of the 1949, 1961, and 1966 amendments to the Act pertaining to those sections in which the term “retail or service establishment” is found, particularly in the section 13(a)(2) exemption; (b) the decisions of the courts during the intervening years; and (c) the Secretary's experience in the intervening years in interpreting and administering the Act. These sources of information enable the Secretary to lay down certain standards and criteria, as discussed in this subpart, for determining generally and in some cases specifically what sales or services are recognized as retail sales or services in particular industries.