<h1>Unjust enrichment principle: refunds require proof duty incidence was not passed on and strict accounting and documentary evidence.</h1> The circular applies the unjust enrichment test to refunds of excise, service tax and customs duty, presuming incidence is passed on except for exports, export inputs and unspent PLA; claimants must evidence non passing by recording refundable amounts as 'Duty Receivable' in Current Assets across relevant financial years, avoid capitalising duty into cost or depreciation, and produce specified documentary and certificate evidence (including supplier and recipient certifications and CENVAT credit reversals). Pre deposits are excluded from this test.