I am not a pro-magi but I thnk those that are would probably benefit from reading sales and marketing books. Here are a couple of good ones.
The Secrets of Word-of-Mouth Marketing: How to Trigger Exponential Sales Through Runaway Word of Mouth by George Silverman
Ths book goes for $12 on Amazon and is worth every penny. I think pros could ue the material to help build a client base and repeat business.
George Silverman just happens to also be a member of the SAM Parent Assembly in NY and marketing consultant by trade. He is really good with coin magic and uses it to hlp impress clients.
Another good book on sales is Sales Don't Just Happen by Stepehen Schiffman.
Really gives you an idea of how to set up appointments with clients and sell them a show.
Neither of these books are aimed at the magic industry but if you get them you will see how they apply.