Where plaintiff in an action to recover commissions for procuring a purchaser for real estate proves the execution of the contract of purchase, which defendant claims was signed conditionally, the burden of proving such defense is on the defendant. Folinsbee v. Sawyer, 36 N. Y. S. 405, 15 Misc. 293.

Property owner and a real estate broker may agree that payment of commission depends upon the making of an enforceable contract between the owner and a purchaser, or condition, payment to be only from the proceeds of the sale. Edward F. Harrington Co. v. Waban Rose Conservatories, 111 N. E. 37, 222 Mass. 372.