If you spend a lot of time in the DA forums, you will see this topic spring up again and again. Whether you want to earn a living doing freelance art, or you just want to do an occasional commission, the following guidelines may help you. For the purposes of this journal I'm going to assume that you developed sufficient skill for potential clients to want to purchase your work. If that is not the case, then get back to studying and practicing
1) Why is it so difficult to choose a price? Why can't someone look at my art and tell me what to charge?
Because your ability to sell something is not just a matter of assigning a price based on your skill level!
If three people can draw the same drawing with the same level of skill, one might be able to sell the art for $10, another might be able to sell the art for $100 and the third might not be able to sell it at all depending on how good they are at "marketing" (seeking out or attracting the best clients and convincing