Where the owners of real estate agreed to sell to a purchaser procured by their broker, and the purchaser paid $10 of the price, the owners were estopped, when sued for commissions for making the sale to assert that because they subsequently refused to carry out their agreement there was no sale. Gwin-nup v. Sibert, 106 Mo. App. 709, 80 S. W. 589. See also Sec. 861.