People do judge people by their covers.  I have noticed a distinct difference in how I am treated when I am in my "uniform" or "costume" (suit and tie) as opposed to my jeans, t-shirt, and ball cap.

Suits and ties are what are expected of me by my clients, like a white coat for a doctor, or a blue uniform by a police officer.  I am often mistaken for an attorney.  The thing is I am treated like someone that should pay more and is afraid to get his hands dirty.  The fact is, I am a big DIYer.  I wear disposable glove to keep paint, oil, grease off my hands . . .

On the other hand, in my regular clothes, I get treated like a regular guy and talked to on a more "real" level.  I am perceived as capable of using tools and equipment . . . same person, different treatment.

All this said, I guess the takeaway is be conscious of this tendency in yourself and others to judge people by appearances only.  I will add you can use this to you advantage by dressing the "part" you need to play-- would you go car shopping in a suit or in jeans and a t-shirt?  Who will probably pay too much?  Think about it.