(6)If, upon information which has come into his possession, the Commissioner is satisfied that any dealer who has been liable to pay tax under this Act in respect of any period, has failed to get himself registered under section 14 or section 17, as the case may be, the Commissioner shall proceed in such manner as may be prescribed to assess to the best of his judgment the amount of tax due from the dealer in respect of such period and all subsequent periods and in making such assessment shall give the dealer a reasonable opportunity of being heard, and the Commissioner may, if he is satisfied that the default was made without reasonable cause, direct that the dealer shall pay, by way of penalty, in addition to the amount of the tax so assessed, a sum not exceeding twice that amount.
