Hmmmm I don't like judging on first impressions, because I've been wrong so many times about people! I do get feelings about people, like when something seems a bit 'off', and that usually turns out to be right but I'm really not all that great at it so I just go with the flow now and to hell with it.
Like your Gav, my Gaz is a fantastic judge of character, maybe it's a 'G' thing?