Which of the following financial instruments is NOT sold by USPS?

The reason why credit cards are not sold by USPS is that they are financial products typically offered by banks and financial institutions, rather than postal services. USPS focuses on providing specific financial services that meet the needs of its customers, such as money orders, gift cards, and money transfer services like Sure Money. These offerings are designed to provide users with secure payment options, but credit cards, which involve a line of credit and interest accrual, fall outside the scope of the postal service's financial products. This distinction highlights the USPS's role in delivering certain financial services while leaving credit-related products to specialized financial entities.