Whenever a transaction occurs in which the customer used a credit or debit card issued outside of the United States, both the International Service Assessment Fee (ISA) and the International Acquirer Fee (IAF) are applied by Visa.While the final charge for the ISA fee can vary, the IAF fee sits at a flat rate of 0.45% of the transaction's cost. There's no other major difference between the two and you will be charged both whenever you process an international payment. You may see them bundled together on your monthly statement or listed separately.