After my Junior year in college, I took a job as a tutor for a private tutoring company. At the time, I had hair that ran halfway down my back, and that is no exaggeration. It wasn't nappy, greasy, or covered in split ends; in fact it was rather well-kept. For this new job, I had to lop it all off, and keep it above the collar.
I had spent many years getting my hair that long, it was a project I had taken some pride in. But I was also in college, and wanted to get a semi-professional job, so off it went. In a sense, this was the first time I really sacrificed the fruits of my labor for a chance at greater gain, as I had played everything very safely throughout high school and the first few years of college. Money was more important than an appearance that I had spent some time working on cultivating, even if it served no practical purpose. I also started the long process of updating my dress to look more professional, since my college garb was plaid shorts and a free t-shirt from Company X or University Department Y.
The impact of this decision was almost immediate. Security guards stopped checking my bag to see if the receipt matched the items inside, restaurant staff started waiting on me better, when I was in the mall I noticed the employees taking some effort to help me find items. I was the same person I was before: I didn't shoplift, I was polite to wait staff and generally left a healthy tip, and I generally didn't go shopping just to browse then buy nothing. The change in behavior was totally in their perception of me, and while you could argue that they should treat everybody the same until given some reason to treat them with more or less respect, it did hammer home the point to me just how important appearances are in the world.
After a few years in graduate school, my dress had lagged back to the undergraduate routine. A very good friend of mine began the long project of getting me to dress nicer, and look as attractive as I could look. It's taken over a year, and I've gone through several iterations of dress, but I've finally settled into a style, and the effect hasn't changed. People treat you differently, even if they have no substantive reason to do so. I get compliments all the time about a sweater I'm wearing, or a sport coat that fits just so, or just the general way I'm dressed for a day. The first day I wore my navy blue sport coat in public, with jeans and a button down shirt, I got three comments from total strangers about how good the coat looks. The truth is, the coat looks good because I make the coat look good, by paying attention to fitting, and what else I wear.
Looking like a smart, well dressed person makes every first encounter with another civilized person a positive opportunity, and a chance to judge each other on the merits of personality rather than something more superficial.