Education deduction(self-employment)

I have read the rules regarding education expenses multiple times, but I'm seeking help understanding this situation because what I'm being told is different from how I interpret the rules.

 

Lets say you don't own your business yet, however the only minimum requirement is to have a high school diploma.  Your current job is in a different field, but you're taking an online course that has components that help you understand the concepts of the trade and how to use the tools you'll need.  It's also going to teach you how to market yourself and your services to obtain clients.

 

Do you need to start your business before you buy the course in order for it to be deductible?  If not, how do you justify this course as an allowable expense?  I have been told it is allowed(as a marketing education expense, professional development, etc)  from more than one person, CPAs included.