The value of the services of a real estate broker for negotiating a lease can not be measured by the value of the fee, regardless of the terms of the lease. Daube v. Nessler, 50 I11. App. 166; Grosscup v. Downey, 105 Md. 273, 65 A. 930. He is entitled, in the absence of a special contract therefor, to a reasonable compensation, and this is usually based on the amount of rental. Schultz v. Goldman, 7 Ari. 279, 64 P. 425; Hull v. Cardwell, 2 N. Y. City Ct. 76.