If on information or otherwise, the Commissioner is satisfied that any person while being liable to pay tax under this Act has failed to apply for registration and to pay the tax, he shall, after giving the person a reasonable opportunity of being heard, assess, to the best of his judgment, the amount of tax, if any, due from him and the Commissioner may also direct that, in addition to the amount so assessed, a sum not exceeding that amount shall be recovered from the defaulter by way of penalty.