Always ask about their experience and background and what types of companies they’ve worked with.
I’m also listing a detailed set of questions to ask during the initial conversation to help you determine if the business coach is qualified or the best fit for you. (You can find other factors to keep in mind here.)

Questions to ask:
How long has the business coach been in business?

How many clients does the coach typically take on?

How much one-on-one coaching time will I get with the coach?

Does the coach offer support between sessions?

Does the coach have experience working with businesses like yours?

What results have clients experienced working with the business coach?

Does the coach have references?

What guaranteed results/promises does the business coach offer?

I usually guarantee the following results:

How long will the coaching engagement be?

What’s the cancellation policy?