When, by the terms of the contract between the trustee and the principal debtor, any mode of ascertaining the value of the property to be delivered to the officer is pointed out, the officer shall, on application of the trustee, notify the principal debtor previous to the delivery that the value may be thus ascertained so far as it may affect the performance of the contract. In other cases the value of the property, as between the principal and the trustee, shall be estimated and ascertained by the appraisal of 3 disinterested men chosen, one by the trustee, one by the officer and one by the principal if he sees cause; and if he neglects or refuses, by the officer. They shall all be duly sworn to appraise the same and the officer, justice and appraisers shall certify their doings on the execution.