When you're shopping for a stage hypnotist, get at least several different price quotes before you make a decision. Don't necessarily go for the lowest one, since hypnotists aren't all equal in their abilities. Quality may drive up the price in some cases.

Believe it or not, there are standards bureaus that regulate hypnotists (stage and otherwise). One is the National Guild of Hypnotists, which has been around since 1951. If you ever have a doubt about a performer, check and see if they're a member.

Keep in mind that not all hypnotists are created equal. Their acts vary, and so does their levels of training, certification, stage presence, and ability to be entertaining. It's up to you to do your due diligence homework before hiring a performer -- or your event might fail.