Why do some non-financial firms rely on revenue from consumer financial products? At several large U.S. retailers, direct revenues from credit card partnerships exceed total operating income. This paper proposes a theory of behavioral cross-selling, in which firms use their access to customers to cross-sell products that capitalize on behavioral biases, such as inattention or forgetfulness. We test our theory in the retail credit card market using data from a major credit bureau. Although retail cards account for only 17% of balances in our sample, they generate 45% of missed minimum payments, triggering late fees. Liquidity constraints cannot fully explain missed minimums: among individuals with multiple cards, nearly half of missed payments on retail cards could have been avoided by reallocating excess payments from other cards. Consistent with the theory, firms in locations with more avoidable missed payments are more likely to offer retail cards and provide larger sign-up incentives. We discuss how behavioral cross-selling can help explain practices in industries such as airlines, auto dealerships, tax preparation services, and sports entertainment.