4% additional customs duty refunds require Form 102, CA certification, and VAT/CST correlation for claims to be processed. Claimants must file Custom Series Form 102 in duplicate with a numbered checklist and receive a simple receipt evidencing filing date; complete claims get acknowledgement while deficient claims receive a deficiency memo and must be remedied within ten days. Required documents include original Bills of Entry/TR-6 challans or scrip debit entries, authenticated sales invoices, and proof of VAT/CST payment correlated to sales. Sales via consignment agents require an agency agreement and CA certification. A Chartered Accountant (statutory or authorised VAT/IT auditor) must verify records and certify that the 4% duty burden was not passed on, providing detailed correlation sheets; vague certifications are unacceptable and may attract action.