Authorize.net sandbox allows real users

Hello s2Mmeber Tech Support,
I have a site which uses wordpress and the s2Member plug to charge monthly access fees. This site has a copy which we use for testing.
In the testing site i’ve setup a test.authorize.net account and turned on sandbox testing in s2Member. However it seems that I have real users stumbling across my test site and it seems that the test.authorize.net account will accept any legitimate credit card (like these users). So these users are able to create accounts on my test site. I was assuming that only certain credit cards would work for the test account and real credit cards wouldn’t be ran through.

Any help would be a great assistance on prevent my prospective clients from accidentally stumbling on my test site and using their real credit cards to create accounts.

Thanks

If you are using sandbox on a test site, you should really be either testing your website offline (locally), or make sure it is in maintenance mode. Allowing users to use the site (and purchase) while testing/sandboxing doesn’t sound like a good practice to me. Even if real cards were rejected, you are leading users to have a negative experience, which is rarely a good idea. They’ll think your website is dodgy or broken, and you’re probably losing customers.