A principal who obtains knowledge from his broker that an intending purchaser procured by the broker is the person of whom he had learned from another source as a possible purchaser, owes to the broker the duty of either terminating the agency or notifying him that he intends personally to conduct future negotiations, and on his failure to do so, the broker is entitled to commissions, although the sale is completed by the owner himself. Carroll v. Pettit, 22 N. Y. S. 250, 67 Hun, 418.