"The roughly 9.5 percent of all U.S. families that are without some type of transaction account (unbanked) are disproportionately represented by minorities. The unbanked often must rely on alternative ways to carry out basic financial transactions such as cashing payroll checks and paying bills....

We model side payments in a competitive credit-card market. If competitive retailers charge a single (higher) price to cover the cost of accepting cards, banks must subsidize convenience users to prevent them from defecting to merchants who do not accept cards. The side payments will be financed...