A broker employed to bring about an exchange may recover commissions from both sides. Conner v. Munsees, 145 N. Y. Sup. 891. A written agreement for the exchange of real property can not be avoided by showing that the agent who brought about the contract was the agent of both parties, when each party knew at the time that the agent was also acting for the other. White v. Immenschuh, 187 P. 667, - Kan. Sup. - .