Self-confidence is the #1 thing you must have when making money. You absolutely cannot be self-conscious.
I know, you still are young (at heart)–will people take a 14, 15, 22, even 65-year-old seriously? When you approach shop-owners to establish your candy-vending routes, when you buy tax liens as a minor and deal with county clerks, when you are cleaning people’s windows, or whenever you are doing anything, you CANNOT give a damn about your appearance. Whether you are old, young, fat, skinny, white, black, male, female, Jewish, Islamic, athletic, nerdy, have acne, wear glasses, or whatever, chances are that you are the only person that cares. Quite frankly, when people buy a product, they don’t care what you look like or what you believe in. (A fundamental principle in life: everyone is so busy worrying about how they look that they don’t have time to worry about how you look. And even if they do have time, they don’t care.)
Without confidence in yourself, you will make no money, because you will be too scared to make any initiative. More important than that, though, is that you have self-confidence in your prices. For example, one of my favorite businesses is window-cleaning (or for that matter, any sort of contracting). As a window cleaner, you might charge $3 a window inside and out, though it only takes you a minute or two. As a beverage vendor, you might charge $1-2 for a water bottle that only cost you 10 cents.
So then you give an estimate, and the customer balks and asks why you charge so much. Or you do your best job, and a customer makes a big deal that you left a tiny speck on a big window. First, you need to understand that some people are very insecure, and only feel good when putting others down to make themselves feel better; some people are by nature cynical, and enjoy questioning others/giving them a hard time. That has nothing to do with the quality of your work, but instead the type of person they are. Second, you don’t need to give people discounts. The going price for water bottles is $1.50; the going price per window is $4-$8. DO NOT say “oh, I’m satisfied with $15 an hour, so I’m only going to charge that much, so like $1 a window.”
You are an entrepreneur. You are taking risks, and you are investing time/money in several areas-buying supplies, marketing, stress, etc. Also, as an entrepreneur, you deserve to make more than $15 an hour, or however much it may be.
Have a rationale for your pricing; if you’re questioned, provide the rationale, or a long-winded explanation (“well, if I gave you a discount, that would be unfair to my other customers”, etc.), and chances are they’ll get over their problems. Some people want to make sure they aren’t getting ripped off, and always challenge the price, but are satisfied when you give an explanation. If they keep up with their challenging, you have plenty of other customers, and don’t need them.
Have confidence in who you are and what you do; you are a business pro, and don’t listen to any criticism other people give. If you take yourself seriously, others will too.