If you create your payment page in PHP and echo the return URL, people may be able to rip you off by viewing your source and going straight to your "thanks_for_paying" page. We have created a solution that allows you to encrypt your entire PHP code AND the HTML output. This way people can't go straight to your return URL and steal your products! Have a look at: http://www.websitecreations.co.nz/codelock for more details.