I wrote an article on this exact question on LinkedIn here: https://www.linkedin.com/pulse/how-do-i-find-good-ceo-coach-mentor-bob-norton/

First make sure they have done what you want to do, multiple times, they are not just a "Certified Coach". Second the size of the businesses they have RUN will determine their abilities. You want someone who has worked in (run) a startup and grown it successfully, not someone with Fortune 2000 executive. VERY different skills set, mentality and style.

As a CEO and Serial Entrepreneur for 14 years I grew two startups to over $100 million in sales. I have coached over 200 CEOs and trained hundreds of executive teams and senior executives in my CEO Boot Camp, Management Best Practices video Series and AirTight Management Systems. I also wrote The Startup Manual for Entrepreneurs to show them how to plan, launch and scale a new business. Read, read, read too. I have read over 1,000 books on business, leadership and management. My top book recommendations are listed here: http://clevelenterprises.com/Recommended_Reading.htm

I coach one-on-one weekly starting at $600/month for startups. Half my rate for profitable and larger companies.