Do you want a coach to improve your managing skills? To hone your sales presentations? Perhaps you're simply confused and want some objective advice. Whatever the reason, if you can't articulate the challenge you hope to tackle with a coach, you probably aren't ready to hire one.
Do you want a few quick sessions? Or a long-term relationship? If you think your issues can be dealt with quickly, let the coach know before signing up. Your coach may have a different opinion on just how many sessions are necessary.
Some coaches require clients to buy a certain number of sessions; others are pay as you go. In either case, get the coach to agree to have a "how's it going" conversation after a couple of months to assess progress.
Ask for three references: a long-term client (to quiz about specific and measurable results); a new client (to get a sense of how long it takes for the coach to start delivering); and a former client (to ensure that the coach doesn't discourage people from leaving the fold). And require the coach to sign a nondisclosure agreement.
Start off with a minor business challenge--a sales pitch to one particular customer, say, rather than an entirely new marketing plan. If you don't get the results you want, move on quickly. The coaching relationship is not likely to improve with time.
Coaches tend to be charismatic and easy to like. But don't let warm personal feelings keep you from scrutinizing a coach the same way you would anyone who gets access to sensitive information about your company--and your life.