You don't have to stamp the appraiser. The appraisal report shall be signed and sealed by two or more certified asset appraisers and sealed by the appraisal institution, so the appraisal report need not be sealed by a chief appraiser. The validity period of the appraisal report is legal, generally one year, and it can't be used after one year, because the appraisal value of this report may change greatly from the value of the appraisal benchmark date after more than one year, so the appraisal value of this report can't be used any more.