It would still need confirmation from both sides.
What's wrong with the honour system? We already sort of use it. Generally, if someone insists on abusing something, or disregarding some commonly-agreed rules, people will stop playing with him / her after patience has run low / out.
To be honest, I don't like the idea of spending too much time installing safeguards just because some people fail to be social enough to respect a few simple, non-or-lightly-restrictive rules and / or agreements.
Also, remember that hosts can kick. And kicking a player removes all interactions with that player (except chatting).
By the way, kicking and internal quitting (the /quit command) are the least tested. I did my best, but I still might have missed something.