1. The consumer didn't ask for the invoice, because some consumers would forget to ask for the invoice or feel troublesome.
2. Businessmen may deliberately not invoice because of tax evasion, so as to achieve the purpose of tax avoidance.
Consumers want to get some discounts or other benefits, so they voluntarily give up asking for invoices.
However, in order to avoid any disputes or problems, consumers are advised to ask merchants to issue invoices when purchasing any goods. Invoice can be used not only as proof of purchase, but also as proof of warranty, maintenance, return and other services. If consumers find that the merchant has not issued an invoice, they can ask the merchant to make up the invoice.