After 10 years as an executive coach I would suggest that you get really clear about what coaching is and what you truly desire in what you're calling a coach. Many self-styled coaches are really educators, workshop leaders, information marketers, consultants or mentors using this decade's buzz word to describe what they do. A coach will help you achieve your goals by building your internal capacity, problem solving abilities, supporting habits and self awareness. A coach will help you formulate questions that expand possibility and will assist you in creating habits that sustain and build you. A great coach will leave you stronger with more capacity and more faith in yourself than when you started.
Be careful of the person who styles themselves an expert in the domain you're trying to improve. Experts tend to offer answers that have worked for others. One of the wonderful things about coaching is that it works to help you find answers that work for and with you, that build on your strengths and get you around any areas that have been challenges for you in the past.
Beware the 3,5 or 7 step process or any 'coach' who promises a blueprint to a promised land.
There can be value in 'program' based learning and 'blueprints' to success but it is decidedly not coaching.
Ask yourself if you're looking for a mentor, a consultant or an accountability buddy. All of these roles have value, but again, are not coaching per-se.
The International Coaches Federation (ICF) website provides a good list of well trained and tested coaches. After that proceed as you would with any professional, ask for references, training schools attended, years in operation. Rather than asking for a 'sample' coaching call ask for a conversation to discuss right fit. When you get the conversation inquire into how the coach themselves determines if a client will work well with them. Newer or less confident coaches will have trouble answering this question. An experienced coach knows who they work well with. Ask specifically how a coach distinguishes between mentoring, coaching, consulting & training and listen carefully to see what it is exactly that you want.
I'd be happy to speak with you regarding right fit if you like.