If the principal refuses to accept the customer furnished by the broker, in an action to recover commissions the broker must prove the customer's ability to complete the transaction. Col-burn v. Seymour, 32 Colo. 430, 76 P. 1058; Fay v. Ryan (I11. Sup. '09), 88 N. E. 974; Dent v. Powell 93 Iowa, 711, 61 N. W. 1043; Russell v. Hurd, 113 I11. App. 63; Coleman v. Meade, 13 Bush (Ky.), 358; Staehlin v. Kramer, 118 Mo. App. 329, 94 S. W. 785; Clark v. Wilson, 41 Tex. Civ. App. 450, 91 S. W. 627; Allison v. Chapman, 173 P. 389, - Cal. App. -; McDonald v. Kimmell, 70 Pa. Super. Ct. 282. Burden on defendant to prove irresponsibility of the purchaser. Cook v. Kronke, 4 Daly (N. Y.), 268.