All appeals are dismissed.

The costs of appeal are assessed against the plaintiffs.

The grounds of appeal are examined.

1. As to the grounds of appeal against Defendant C, the Plaintiffs filed an appeal against Defendant C (hereinafter “Defendant C”) of the lower judgment, but did not state the grounds of appeal in the petition of appeal and did not state the grounds of appeal as to the grounds of appeal.

2. As to the ground of appeal against Defendant KB real estate trust company

A. In a case where a party to a contract directly provides a third party who has a different contractual relationship with the other party by shortening the performance process through the instruction of the other party to the contract (in a case where the performance has been made in a deceptive relationship), the other party to the contract may not claim a return of unjust enrichment on the ground that the party to the contract received the payment from the third party without any legal ground, as well as the performance from the other party to the contract has been made.

In such a case, if a party to a contract can make a direct request for return of unjust enrichment against a third party on the ground that the contract was defective, such as invalidation, etc., in a legal relationship between a person causing the performance of a contract against the contracting party or the contract was cancelled, it would not only bring about a result contrary to the principle of contract law by transferring the risk burden under a contract concluded under his/her own responsibility to a third party, but also unjust because a third party, the beneficiary, has infringed

(Supreme Court Decision 2001Da46730 Decided December 26, 2003, and Supreme Court Decision 2014Da77956 Decided April 23, 2015, etc.) B.

1. As to the claim for cancellation during the primary claim, the lower court, inasmuch as Defendant C sold the instant commercial building by specifying its use as a fishery products distribution center under each of the instant sales contract, has a contractual obligation to provide commercial buildings by establishing its basic facilities.