You deserve to charge employers and clients what you're worth. If your self-image makes it hard to accept that sentence, then consider an alternative: If you charge less than what you're worth, people might think that the services you offer aren't that good.
As business site Entrepreneur points out, we all have a natural tendency to assume that if something costs more, it must be worth more. After all, there must be some reason that watch costs $US10,000 ($12,971), right? Well, the same principle applies to your salary. If your work is worth $US50,000 ($64,856) a year to the company, but you're willing to accept $US25,000 ($32,428), your employer might assume that the work you do isn't very good:
I've run split-test campaigns on e-learning courses for a company I was doing some consulting for, and one test still stands out to me. We tested two price points for a digital course. We tested a low price point of $US37 ($48) and a higher price of $US397 ($515). Which one do you think performed better?
The higher priced campaign sold three times as many courses as the lower priced test. Why? That's simple — people automatically associate higher prices with higher value.
The same can apply to freelancers as well. If you take a commission and try to put out the lowest price to attract as many customers as possible, you might accidentally give the impression that the work you do is low quality. If your work looks low quality, then you get fewer customers, and you never offset the difference in volume. It may go counter to your own self-perceptions but sometimes it's better to aim higher.