S.D. Codified Laws § 35-8A-3
Any supplier and any wholesaler may contract with one another to establish the terms and conditions of their distribution arrangement. If any supplier and any wholesaler have entered into a mutually binding written agreement, the provisions of this chapter do not apply and the relationship, rights, and obligations as between the parties shall be governed in all respects by the provisions of the mutually binding written agreement, if the provisions are reasonable, nondiscriminatory, and not unconscionable. However, no provision of a mutually binding written agreement that is determined to be unreasonable, discriminatory, and unconscionable is of any effect, and the provision is severable from any other provisions. Any specific provision in the agreement is invalid if the provision is more restrictive of the wholesaler's right than this chapter allows or if the provision lessens any obligation of the supplier as specified in this chapter; in that event the provisions of this chapter apply. A supplier may have a different agreement with different wholesalers in different brands.
In the event of a dispute as to whether the relationship, rights, and obligations as between a supplier and a wholesaler are governed by a mutually binding written agreement or by this chapter, any court of competent jurisdiction in this State may determine the issue by declaratory judgment upon proper application to the court by either party to the dispute.
SDCL 35-8A-3