Generally speaking, an agent cannot bind his principal to a contract with a third person unless the agent acts within the scope of his express, implied, or apparent authority.
In a purchaser's suit for specific performance of a contract to sell real estate made by an agent of the seller, the burden of proving the agent's authority to enter into the contract is upon the purchaser. Vogler v. Dyer, 149 Ark. 670 (mem.), 234 S.W. 504 (1921). It is well settled that the authority of an agent must be shown by positive proof or by circumstances justifying the inference that the principal has assented to the agent's acts. Mack v. Scott, 230 Ark. 510, 323 S.W.2d 929 (1959). A person dealing with a known agent is not authorized under any circumstances to blindly trust the agent's statements as to the extent of his power; such person must not act negligently, but must use reasonable prudence to ascertain whether the agent is acting within the scope of his powers. First Pentecostal Church v. Koppers Co., Inc., 280 Ark. 101, 655 S.W.2d 403 (1983).