Applications to lease or purchase state lands shall be made under oath, and applicants to lease shall, at their own expense, procure appraisements thereof to be made under oath by some disinterested and creditable person or persons familiar therewith. All statements contained in such appraisements, except as to the true value of the land appraised, must be based upon personal knowledge and not upon information and belief. No such appraisement shall be conclusive upon the commissioner.