Your assertion doesn't even make 1st base by simply considering cashier = owner, as is the case of many small businesses; it conflates one possible usecase as the only valid usecase.
Receipts may also be required by law (which still supports "the receipt is not for the customer")
Furthermore, a business that accepts returns is the cost paid to increase customer confidence; it's called risk mitigation. Any return accepted is revenue rescinded and indirect cost incurred by the business to restock with the aim of winning future conversion.
A business issuing receipts as required by law is a consumer protection mechanism; a business retaining its receipts is for tax compliance.