It's a chore to vet all applicants, but that goes with the territory.
Vbulletin offers ISP/Domain blocking, various hurdles etc for new members, and still we get lots of scammers trying to register to get into our stationary engine forum. As all applicants have to be manually approved as well as all the other hurdles, we keep most out.
We also get the morons and the clueless that can't answer a question about the capital city of a US State, or how many in a Baker's Dozen, then email me and complain!
Such is life.
Peter