How much and to what extent all depends on too many factors to list. Just a few are how old they are, what kind of money might they have (ie what other things might take more of their money than their clothes).
Probably the biggest thing that makes me judge based on clothing is if they are trying too hard or trying to be 'cool/edgy' often like everyone else
This doesn't mean I discount them or won't let them actually show me who they are but it can be a 'strike' against them until I see who they are.
We all do it on some level. Even when we don't think we are doing it. But how much you judge is where people differ. I don't think what you wear is the single most important aspect in the type of person you are, but what you wear does say something about you. If a girl with big tits walks into a room, with a low cut shirt during lunch hour, every person in the room judges her a bit.
Would I? Probably. Would I care? Nope. Everyone is free to to whatever they want. Got nothing against Goths, but fuck some of them dress up in very creepy lolita way which makes me go "What the fuck is wrong with you? You're like 20 or something and dress up like some pedo-bait..."
Well of course. I'm not going to try to change their style or make fun of it because its not really any of my business on what a person is to wear a not. But the way you dress and present yourself with fashion can really be important especially with first impressions. So of course if they dress very lazily and just like they threw it on, it doesn't say a lot of good stuff (for a job interview for example), it gives the impression they don't care. So fashion is very important.
Lol, people judge me all the time just because they think "I dress like a prude." They think I don't like to have fun or anything. It gets really annoying. I dress in comfortable clothing and I also have insecurities about my body, but that doesn't mean that I don't like to have fun. I wouldn't judge someone on what they wear. What they wear doesn't matter.
I would have to say yes and no. I typically go off the colours and actual representation (actual WEARING) of the clothes. If they wear black clothes, I'll assume they're either feeling down or like black lol If they wear it sloppily I'll assume they are tired, high (not racist cuz my school is ghetto lol), or just stopped caring. Of course any time I take enough time to assess someone else I plan on speaking to or getting to know them better in the future.