Special audit authority requires nominated external audit of records where declared value or input tax credit appears irregular, enabling assessment action. Special audit may be directed where an Assistant Commissioner-level officer suspects incorrect valuation or abnormal input tax credit; the Commissioner nominates a chartered or cost accountant to audit records and submit a signed report within ninety days, extendable for cause. The audit requirement applies notwithstanding other audits, the taxpayer has a right to be heard before audit-derived material is used against them, the Commissioner fixes and pays audit costs, and detection of unpaid tax, erroneous refund or wrongful credit may prompt assessment or recovery proceedings.