[steve-b]

smart magicians pay their assistants very well. For one thing in most stage tricks it's the assistants that do most of the real work, and a lot of it is really uncomfortable (the hiding holes for various disappearances/ transformations tend to be rather tiny). For another they know how all the tricks work, there's nothing quite like a disgruntled assistant to help some other magician's career.

Also, the assistant's stage presence and looks are critical in drawing the audience's attention away from the magician when he makes his hidden move.

[discostu]

yes the old "the long leg hides the small action" rule. Though really hot chicks you can throw on stage as a distraction are a dime a dozen, hot chicks that can fit themselves in the tiny little basket of a metamorphosis trick in the 10 seconds they have before the curtain drops tend to be a bit more pricey.