Where, in an action by a broker for commissions, the evidence showed that he was to receive $2 per acre from the owner, if he received for his land $16 per acre, or the amount per acre in excess of $14, in case the owner did not receive $16; that the owner exchanged his land for other land, and that the contract for the exchange fixed the price of the owner's land at $16 per acre and the land received at $45 per acre, the owner could show the value of the land received in exchange to enable the jury to determine whether or not he had received more than $14 per acre for his land. Steers v. Gingery (S. D. '07), 110 N. W. 774. See also Sec. 1076.