Most of the uninitiated have an image of hypnotists as mysterious men, waving pocket watches about and turning their victims subjects into zombie-like states.
Once they're hypnotic state, subjects are compelled to obey, no matter what. And, of course, they must utter the obligatory “Yes, master”, as they carry out the control hypnotist's evil demands.
Hypnosis is a collaborative process, that is to say you have to be willing to take part. Generally, people won't do anything which goes against their personal values or beliefs. If someone tries to tell you to do something that is really against your own values, you won't do it. You'll naturally come out of the state of hypnosis.
Hypnosis is a strange art that for the most part involves a suggestible state where the person under hypnosis is more likely to listen to suggestions by the person performing hypnosis. And it turns out that some people are considered more suggestible than others.
Scientists have performed studies that confirmed not only that some people have higher hypnotic suggestibility, but that those people are also likely to get a lot more out of hypnosis than those who are not. It is important to note that the same researchers believe that for those who are considered to have low suggestibility, that hypnosis is probably not a very useful option.