(A) The tax commissioner shall promptly determine the correctness of the return with respect to the includibility of property, the fair market value or, if applicable, the actual qualified use value of the assets included in the gross estate, the allowance of the credit against the tax and deductions, and all other matters necessary to determine the correct amount of the tax. For this purpose, he may issue subpoenas, compel the attendance of witnesses and the production of books and papers, examine the witnesses under oath concerning any relevant matter, and require the submission of affidavits and forms which he may deem necessary to determine the correct amount of the tax. The tax commissioner may designate an employee or employees of the county auditor or of the probate court of any county, with the consent of the county auditor or of the probate judge of that county, as his agent or agents to assist him in accepting filings of returns in the county, in determining the correctness of the returns filed in the county, and in complying with this chapter. The employee or employees so designated shall have all of the powers granted to the tax commissioner for these purposes.