Owners of property often leave it for sale with several different brokers at the same time; in such cases the several brokers have concurrent authority to sell, but a sale by one of them, with the knowledge of the others, puts an end to the agency of the others by removing the subject-matter of the agency; since they can have no further power than their principal has, and he having, by his agent, once sold the property to one person, can not rightfully sell it again to another. Cushman v. Glover, 11 I11. 600. See also Sec. 15.

Where an owner employed a broker to procure a purchaser for a commission in excess of a specified sum received for the property, and the broker, without authority, employed a third person who brought about a sale for more than the specified sum, and the owner accepted from the broker the specified sum and conveyed the land, without knowing that the third person had claimed to act as his agent, the owner was not liable to the third person for commissions. Beriham v. Ferris, 124 N. W. 538, 159 Mich. 632; Belden v. Kellwood Realty Co., 131 N. Y. Supp. 580, 74 Misc. Rep. 61.