I was so excited to find this course for sale.  I am an instructional designer and even though I have not created and sold my own course, I have helped a client build and publish a course on Udemy.

What I know to be true, is that your best earning potential comes from promoting your own Udemy course once it is published.  They pay out a smaller commission to you if someone finds your course organically through their search, rather than you driving customers to your course for them.  

The sales model is solid in the sense it creates reoccuring revenue for courses that people choose to buy.  However, doing your own promotion is the way to go.

I hope this audio course gives you the opportunity to explore whether this is a way for you to generate income.  I didn't write this one but I do have experience in this area, and purchased it, because it is a question I get often when people find out I am a course creator.