Such certificate shall be signed either by the selling dealer himself or by a person duly authorised by him in this behalf.

No deduction from turnover of resales of goods purchased from other dealer except on certificates There shall not be deducted from the turnover of sales, the resales of goods purchased by a dealer from a dealer registered under the Central Sales Tax Act, 1956 and who is liable to pay tax under section 4, as provided in sections 7, 8 and 10 unless the dealer claiming deduction produces a bill or cash memorandum containing a certificate that the selling dealer is liable to pay tax under section 4 on the sale of goods to him and that the said sale is in the course of business of the selling dealer.