... is that I'm talking about whether you "do" know, with some degree of certainty, what another's attitude is, not whether you "think" you know. We often think we know what's behind anothers actions, but all we're really doing is assuming they have similar thought processes as us.

You can choose what signals you send consciously, which may engender a false belief in another. Given this, the smart thing to do is ignore the obvious messages and look for evidence that can't be faked.

As regards dress codes, if I saw two people in a professional services company, one dressed in suit and tie, one in jeans and t-shirt, I'd pick the second one any time. That's the person who is employed "despite" their dress sense, and so are probably very good at what they do.

This has served me pretty well over the years and usually points me to the person that really knows their stuff rather than the ones that just have the certs and know how to look the part.