To be fair, it's not easy to catch any but the stupidest cheats, who simply open new accounts from the same IP address.
Playing from the same IP address is allowed. Playing from the same computer isn't, unless the 2 accounts don't interact and admin are informed. If you watch over time, lots of people get banned for multiboxing, then a couple of days later they're back in the game. Always seems to be big Russian players, but I have seen others too. The game is corrupt, they make it too easy to get the ban overturned, so people will continue to do it. The only way it will stop is if they start being stricter with the rules.
And you're correct, there are lots of low level accounts made up just of spies and visionaries. Most of these will be multibox accounts, but until they actually get caught doing something against the rules, there's not much admin can do. And even when you do report somebody for multiboxing, they say "tell us when so and so happens", you then do that and they say "should have taken some screen shots". Would have been nice to be told that originally...