No sale of real estate at private sale or sale by negotiation shall be confirmed by the court unless the gross sum offered is at least ninety percent of the appraised value thereof, nor unless such real estate shall have been appraised within one year immediately prior to such sale. If it has not been so appraised, or if the court is satisfied that the appraisement is too high or too low, appraisers may be appointed, and they must make an appraisement thereof in the same manner as in the case of the original appraisement of the estate, and which appraisement may be made at any time before the sale or the confirmation thereof.