This took me a long time to realize because I was never one to follow trends or fashion, but people make a choice when they dress themselves. The manner in which you dress yourself says how you want to be represented.
I'm not sure if I would reject a guy solely on his attire, but I would judge him on it. I don't like admitting that I judge people so shallowly, but how someone dresses really speaks for how they want to be interpreted.
Say for instance a person in full on goth attire approached me. I think I can assume merely from his look some of things he believes in. Of course, I wouldn't any assumption against him, and I would be fine with getting to know him better. Same goes for a guy who is dressed entirely in designer labels. Or a guy who is dressed in a pair of jeans that 3 people can fit into. They are making a statement about themselves by how they dress.
If I am approached by someone I do not know, the only basis I would have for evaluating him at all would be on his appearance.
I'm not sure what you mean by if I didn't like the way he dressed. Because if he just had no style, then no I would not reject him. But if the style he has is a style I don't like (emo, goth or whatnot) then yes. I know I'm gonna get a lot of thumbs down for that but, just as kateakanne said, you will get judged on the way you choose to dress.