In an action by a real estate broker for commissions, it was error to tell the jury, in answer to a question by their foreman, that they were not bound by any rule in fixing damages, as the court should have charged them that the rule was the customary commissions in such cases, or, if the evidence was insufficient on that question, what would be a fair compensation. Hartman v. Warner, 75 Conn. 197, 52 A. 719. See Sec. 300.