Refund entitlement under Section 11B requires proof that duty incidence was not passed on; interest follows delayed payment. Refunds of excise duty are governed by Section 11B, with interest under Section 11BB where refund is delayed. Claims must be filed in prescribed form with supporting documentary proof that the duty incidence was not passed on; if incidence is passed on, refundable amounts are credited to the Consumer Welfare Fund. The claimant bears the burden of proof and unjust enrichment is assessed case by case. The manual prescribes filing, scrutiny, sanction and payment procedures, concurrent processing during appeals, and pre/post-audit and monitoring mechanisms including special rules for deposits, diplomatic missions and statutory exemption notifications requiring expedited refunds.