As far as I understand it, if you have a website with a non U.S. domain name and not using a U.S. or U.S.-treaty-based payment system, there is no way to block access to rip-off items (material or digital) to be purchased in the U.S. For material goods, customs have the ability to confiscate these at the borders. There are international treaties in progress, where the U.S. partners with other countries, but the internet is a big, wide-open place and it's easy to move elsewhere or get safe harbour.

(For the record, I believe that only innovation will solve these problems, not suppression).