Would it be possible to block Tor users? (https://www.torproject.org/)
Due to the nature of the site I run I should do all I can to stop multiple accounts and block cert
Yes, and in fact here is a script that will do it for all of your windows machines. Like others mentioned above, it's as simple as blocking all the exit nodes, but that takes a little work.
https://github.com/Austin-Src/BlockTor