The coaching industry is young, and to date unregulated. Just about anybody can hang out a shingle that says "Coach." So let the buyer beware!
There are formal professional standards for coaches that are spelled out in a set of Core Competencies and a Code of Ethics established by the International Coaching Federation. These call for training in proven techniques that allow a coach to create awareness in clients, help them design actions, plan and set goals, and manage a client's progress and accountability.
If you look for a coach that has completed ICF accredited training, then you can expect the coach to exhibit a high standard of performance, a clear understanding of the coaching process, and professional behavior.