SDCL § 59-5-2: Agent's responsibility as principal.

One who assumes to act as an agent is responsible to third persons as a principal for his acts in the course of his agency, in any of the following cases, and in no others:

(1) When, with his consent, credit is given to him personally in a transaction;

(2) When he enters into a written contract in the name of his principal, without believing, in good faith, that he has authority to do so; or

(3) When his acts are wrongful in their nature.