That the broker employed to procure an exchange of property for defendant produced a person purporting to act as agent, with whom defendant effected an exchange, the broker could recover commissions without showing that the person with whom defendant exchanged property was, in fact, the agent of the purported principal, defendant, by contracting with the person produced, having relieved the broker of responsibility for the agent's authority to make the exchange. Callister v. Wichern, 131 N. Y. Sup. 611, 147 App. Div. 14.