I have met him before (several times), and he was always well-behaved during bookings with me.
However, I decided to not let him have another repeat visit, because (TMI alert) his breath is so unbearably rotten, that I simply couldn't put myself through it one more time, not even for 5 seconds.
Last time we met was about 2 and a half years ago, and since then I have not responded to any of his texts/e-mails, yet to this day he still sends booking requests, often using different usernames ( I can still see it's him, as they're all linked).
I don't know whether or not he has the potential to become dangerous, but I know for sure that he's a nuisance, and doesn't recognise a simple hint i.e. when somebody ignores you for 2+ years, they probably just want you to go away!
All in all, just not worth the hassle, plus his breath really is the worst thing ever ;/