The simple answer is, anyone of normal intelligence who has the desire and will to be hypnotized. Experts agree that all hypnosis is self hypnosis. The hypnotist guides you into the state where you are receptive to positive suggestions for change. Hypnosis enables you to bypass the critical part of your mind to access the subconscious mind where all your beliefs, habits, and behaviors are stored.
Trance is a natural state that we experience in our daily lives. It can be compared to what you experience just before you fall asleep. You are aware of your surroundings and hear what is said. You will feel that you are in a contented space with your eyes closed.
No. When you are hypnotized you are aware of the suggestions that are given to you. You will always have the ability and freedom to accept or reject any suggestion made. Consequently, you are in control.
There is no danger of a person failing to come out of the hypnotic state. You would either return to alertness if you no longer heard the hypnotist's voice, or would drift off into a natural state of sleep and would awaken after you rested.