means the related activities performed (either through unified operation or common control) by any person or persons for a common business purpose, and includes all such activities whether performed in one or more establishments or by one or more corporate or other organizational units including departments of an establishment operated through leasing arrangements, but shall not include the related activities performed for such enterprise by an independent contractor: Provided, That, within the meaning of this subsection, a retail or service establishment which is under independent ownership shall not be deemed to be so operated or controlled as to be other than a separate and distinct enterprise by reason of any arrangement, which includes, but is not necessarily limited to, an agreement, (a) that it will sell, or sell only, certain goods specified by a particular manufacturer, distributor, or advertiser, or (b) that it will join with other such establishments in the same industry for the purpose of the collective purchasing, or (c) that it will have the exclusive right to sell the goods or use the brand name of a manufacturer, distributor, or advertiser within a specified area, or by reason of the fact that it occupies premises leased to it by a person who also leases premises to other retail or service establishments * * *