Waste of money. Too much TV and ficton novel hype about what hypnotism really is and how it works. Most advertised hypnotists got their training in a weekend seminar or from a DVD. Most certifications are from groups with absolutely no credibility. And a D.Hyp or some such degree is purely diploma mill.
Many are worthless because anybody can call themselves a hypnotist. But I quit smoking abruptly and effortlessly after visiting a hypnotist for one session, back in 1976.
You really need to find one who's qualified in the field. Usually a good therapist will have that certification, but try to find one who uses positive messaging vs. negative...
An example would be saying "You are a healthy happy individual with beautiful pink, chemical free lungs that enjoy each oxygen filled breathe you take"
instead of " From this moment on, you will be repulsed by cigarettes and feel sick if you smoke"
Positive should override negative
as Asukuku said, they can help.
So if you feel its necessary, get hypnotised :--)