On or about May 1, 1962, Daniel Partin offered to sell Earl and Billie Walker (defendants) a water softener for use on their dairy farm. Partin represented that the treated water would increase milk production. Partin and the Walkers orally agreed to a trial run of the softener. The Walkers would purchase it if its use did in fact increase milk production. If it did not, Partin would remove the softener and the Walkers would not be obligated to pay for it. Concurrent with or after the parties’ agreement to the trial run, they entered into a written sales contract for the softener. The contract provided that the Walkers would make payments in monthly installments beginning June 6, 1962. Partin orally agreed not to assign or transfer the contract. The softener was installed. During its trial period, Partin assigned the sales contract to Associates Loan Co. (Associates) (plaintiff) and sold his business to Stirman Rivers. The trial run was unsuccessful, and the Walkers did not make any payments. Associates brought suit. The Walkers prevailed in the trial court, and Associates appealed.