Where the contract between the broker and his principal is oral, and its terms are in dispute, it is error to instruct the jury, that if the plaintiff brought the purchaser to the notice of the seller he is entitled to commissions, and that that was the only question for them to determine, unless, under the only reasonable interpretation of which the language of the parties was susceptible, in the light of the circumstances, that was all he was required to do to earn the commissions. Henderson v. Sonneborn, 30 Pa. Sup. Ct. 182.