Is it possible to verify identity of site that sent request to you? Code for creating widget may be placed to several places. The easiest attack may be to place this widget to localhost and then reload it many times. But I don't want to pay for such requests as it's not even rendered on site where it should be. There is no problem for me if widget isn't placed at traget site (No views => No pay). There is a problem if it will be placed somewhere else except target site.