Recourse for unexplained return discrepancies: officer may order audit, special audit, inspection or tax determination. If a taxable person fails to provide a satisfactory explanation within 30 days (extendable by the Proper Officer) or fails to take corrective action after accepting a discrepancy under section 45 of MGL, the Proper Officer may: conduct an audit under Section 49; direct a special audit under Section 50 by a nominated Chartered Accountant or Cost Accountant; undertake inspection, search and seizure under Section 60; or initiate tax determination proceedings under Section 51.