Hi all, a few thoughts:
Currently members receive a validation email they have to click on to complete their sign-up, so there is a form of validation at the moment. Unfortunately, this doesn't stop people from using multiple IDs or throwaway email addresses.
Knowing if a person is "genuine" is very difficult, and it depends what you mean by genuine - trolls, spammers, returning banned members?
An email address is attributed to one username, so nobody can sign up with that email address to create another account - it's impossible.
Anyone who goes user inactive and wants to be reactivated needs to ask the editors to do this for them, and we decide if we do it on a case-by-case basis. So if a troll went UI, we would review and not reinstate them if they asked.
We can block user IPs which does work in some cases. But most people have dynamic IP addresses, which means the IP can change at any time - for example if you were to reset your home router your IP address may change. People who really want to get around this also use VPNs which means that we can't block the IP address because other members are also using that IP address so to ban one person would be to ban lots of genuine members.
As an aside, a comment that has since been deleted states the people who run the site don't live in the UK, which was said with misplaced confidence and is completely incorrect.
As previously said, the best thing to do with trolls is ignore and report.