Assessment of non-filers permits officer to determine unpaid GST to best judgment, with withdrawal if valid return filed promptly.

The provision empowers the proper officer to assess a registered person who fails to furnish required returns despite notice, determining tax liability to the best judgement based on all relevant material and issuing an assessment within the statutory limitation period from the annual return due date; if a valid return is subsequently filed after the assessment, the assessment is deemed withdrawn, but interest and late fee liabilities continue to apply.

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