In an action against their principal for damages for the loss of commissions caused by the refusal to accept the deed and carry out the contract where the defense was want of mental capacity to contract, evidence of the actual value of the property is competent only when offered to show that the price offered was so exorbitant as to be inconsistent with good faith on the part of the broker in undertaking to contract for the purchase at the price authorized. Cavender v. Waddingham, 5 Mo. App. 457.