I think it is something most freelancers learn the hard way! My first job I charged $20 an hour when the cheapest alternative was $100. I did everything the way he asked and then had one of his employees call me on a Saturday to have me undo all of it because she didn't like it!

After many years, I have finally learned that the people who balk at paying professional rates are going to be a PITA about everything --- and get it all in writing, as specific as you can be, and get their sign off, even if it is just an email reply, and get 50% up front. So many things to learn the hard way