Hi Ray,
Thanks for the compliment on the cart! What is the specific error that is being returned on international credit card transactions? The cart doesnt have a switch to turn on/off internation credit card transaction but both Auth.net and your merchant account have fraud parameters that allow turning on/off international credit card transactions. Additionally, your merchant account has a black list of card ranges that it checks against and also many other fraud parameters like velocity and certain locales that will result in a decline. The first thing I would do is call Auth.net have them verify that international addresses are not turned off at the gateway. Second, you should call your merchant account company and have them verify that international addresses are not turned off in your merchant account. While you have your merchant account company on phone give them the transaction id and credit card info for one of your international credit card transactions that declined and ask them if they can tell you why it was declined.