Knowledge can help prevent you from getting ripped off as you work in this industry. The reality is that people are going to pay big for beats that are fantastic and will not mind paying less for average beats. Some people will charge around $1.99 for beats and others may charge $50. On a much bigger scale, beats can probably sell for anywhere from $300 to in the thousands. You will really do whatever you can to sell them for.
As you get more well known, you have more to offer an artist as well.
For example, I provide free music promotion whenever an artist records a clean song off a purchased beat from me.
Do I have to do this? No, but it's an extra incentive for an artist to buy beats from my store. That way, I can justify my worth and the prices I charge for beats (which I still think are too low given the value provided!)