This paper provides a theory on how to regulate the level of merchant fees in credit card markets. In particular, we discuss how to regulate the merchant fee in a closed payment system with heterogeneous merchants. We find that tourist test is not a valid approach. Our model suggests that the regulation should be based on costs of networks or banks and market elasticity. Moreover, we provide an alternative understanding on how to regulate the interchange fee in an open payment system. The initial public offerings of Visa and MasterCard do not merely change themselves from not-for-profit associations to for profit companies, but also change the mechanism in determining the fee level and structure borne by end users. These changes in industry urge an updated understanding of the optimality of interchange fees.

中文翻译：

---

信用卡市场中商家费用的规定

本文提供了有关如何规范信用卡市场中商户费用水平的理论。特别是，我们讨论了如何在异构商户的封闭支付系统中调节商户费。我们发现游客测试不是有效的方法。我们的模型表明，监管应基于网络或银行的成本以及市场弹性。此外，我们对如何在开放式支付系统中调节交换费提供了另一种理解。Visa和万事达卡的首次公开发行不仅将自己从非营利协会转变为营利公司，而且还改变了确定最终用户承担的费用水平和结构的机制。行业的这些变化促使人们对交换费的最优性有了新的认识。