Where a dealer makes sales of pre-used motor cars, on or after 1st day of October, 2006, to any person, whether a dealer or not, in West Bengal, such dealer may, for the purpose of determination of his turnover of sales on which tax is payable, deduct under caluse (c) of sub-section (1) of section 16, from his turnover of sales fifty per centum of that part of turnover of sales which represents sale of such cars and he shall, on demand by the appropriate authority under the Act, furnish the relevant tax invoice or invoice or cash memo or bill and other related documents evidencing such sale:

Provided that no such deduction shall be allowed unless the dealer selling the goods, on demand by the appropriate authority under the Act, furnishes the relevant tax invoice or invoive or cash memo or bill and other related documents evidencing such sales.