A written agreement entered into by plaintiffs' customer for the purchase of property and reciting the payment of part of the stipulated price to plaintiffs, is admissible as tending to show that plaintiffs rendered services in effecting a sale of the property. Rothschild v. Burritt, 47 Minn. 28, 49 N. W. 393; Tebo v. Mitchell, 5 Pennewill (Del.), 356, 63 A. 327; Carl v. Wolcott, 156 S. W. 334, - Tex. Civ. App. - . 658