Classical hypnosis was based heavily on hypnotic suggestions, where the hypnotist "convinces" the unconscious mind by suggestion and repetition to change the behaviour to the one desired by the client. These suggestions could be something like this "You are a non-smoker", "You do not crave cigarets", "You are happy about you decision to quit smoking". Through time some hypnotists adopted techniques that were more "Therapeutic" in the sence that they involve re-interpretation of past experiences and parts-therapy. To be able to distinguish between the two strategies for conducting hypnosis and to futher separate stage hypnosis from clinical hypnosis, someone thought of the word hypnotherapy as something done by a hypnotherapist.

Not all hypnotists like this word, especially since a hypnotist is not an officially recognized therapist. To avoid sending those signals, some hypnotists only refer to themselves as hypnotists conducting hypnosis, even though others would classify their methods as hypnotherapeutic techniques. This makes it a bit difficult to separate classical hypnotists from modern hypnotists, who apply methods that are said to be more effective.

A good rule of thumb when you are looking for a hypnotists, is to check his or hers certifications. A certification at NGH (National Guild of Hypnotists) ensures you that the hypnotists as a minimum have gone through the training required to achieve this certification. To continue the membership of NGH the hypnotist must educate himself each year to keep his NGH approval. In the US there are other certifications that ensure similar standards, but be aware that some certification programmes allow for home study of hypnosis!

For those who want to know more, here's an article on the difference between hypnosis and hypnotherapy.