You sort of have it correct.
Basically, a Sythe account is the most secure thing we have. It's the most "unhackable," if you will, means if identification. Everything branches off of there. If someone loses their Sythe account, they're fucked. But that can be identified and their account banned immediately. So while it's the most important, it's also the most secure, because it's completely under our control. Say if someone's messanger goes rogue, then we can't do anything about it other than announce, which still leaves members potentially at risk.
Requesting a private message if you're talking in an outside source allows you to verify that they are who they say they are on our website, which links all of their vouches (a form of reputation here) and previous trades and activities.