Section 7. The appraisers shall be sworn, before a justice of the peace or the officer, faithfully and impartially to appraise the land shown to them as taken on the execution, shall, with the officer, view the same and shall make such examination of it as may be necessary to form a just estimate of its value. A certificate of their appraisal signed by them shall be endorsed on the execution; but if one of the appraisers who was sworn and acted with the others refuses to sign the certificate, the certificate of the others shall be sufficient.