Some of it is guesswork, and some people are stalkers who hunt down multiple users to expose them, a sort of ABer-igilanty. Some people have multiple user names so that they can have a conversation between themselves, often controversial in order to incite rebuke from other users, but mostly just sad and desperate. How other people tell I don�t know, but occasionally they trip themselves up or are just intentionally nasty and knowing without reason or erudition. It goes on of course, but the question is � does it really matter in the grand scheme of things?