My working assumption has always tended to be, words mean what they mean.
Another is, a person is what they do. What they say–in this case, type–is an observable facet of what they do, not the entirety.
I don’t understand why you (generic “you” here, applicable to…whoever it may apply to, not applying to everyone else) would ever feel the need to “judge someone” by what they’ve posted. Evaluate the posts and their contents instead–that’s the facet you’re able to. Some posters may assume airs, trying with varying degrees of success to sound brighter, more interesting, etc., than they “really” are. Others write with a more honest voice. None of that matters much, though–what matters is the content of what they write. Should you start meeting with them away from the boards, then further aspects of them matter as well.
As far as “reading into” goes, that’s just part of human nature. It’s a balancing act between empathy and projection, with the latter always being easier (and thus more common). My own working assumption to combat that tendency is, words mean what they mean. When someone writes something, it’s because they intended to write it using those words, at the time they did so.
It’s no stretch of the imagination to realize that there’s probably quite a few people who would take some umbrage at that philosophy. And that’s understandable, too. What I think balances it out is the “at the time they did so” portion. Held to, it minimizes silly things like grudges and ongoing feuds.
It’s all a great big “it depends”. In my case, I would think most people could tell by my style a few things: I don’t flirt much, I have a tendency to ramble, spend a lot of time being quiet, punctuated with non-sequitors, an overfondness for parenthetical remarks that pepper run-on sentences like tripwires, occasional impatience when people do trip up and fail to follow along, and that I like to club baby seals.
Well, one of those might not be a valid reading-into.
Anyway, the single most reliable thing you can tell about someone from their postings, is whether or not you’re personally interested in reading what they have to say regularly. All else is conjecture.