Doug Henning was on Broadway when I was a student in NYC. Most of my friends were studying acting around the city. Many of them took turns as "audience volunteers" in The Magic Show.

They would que up at the box office early to be "pre screened". They would get a briefing and sign a non disclosure agreement. Then they would run home, clean up and tell all their friends and family, and return.

It worked on a couple levels. First, as aspiring actors, the kids all took the non-disclosure very seriously. Disclosure would violate their eligability for the unions. They weren't afraid of legal action. The Magic Show was a union production. These kids wanted into the union. They didn't want to be black balled.

Second, the pre job brief focused the kids on their role as credible volunteers. It effectively distracted them from focusing on the illusions.

Third, they called all their friends and family. Anyone who could came to the show.

The whole pre selection process was very calculated. It had a very strong effect. It still does. Television shows that use live audiences still do it to some degree or another.

I can see the next trend in magic:

"If you are a aspiring magician or mentalist who cannot get a trick right, the STOOGE 2.0 system is for you. They are not your ordinary stooges, they are specially trained actors who are bound by a legal agreement not to expose their condition, even in front of a judge. They can say "three of clubs", or any other predefined card, when you say "think of a card". They can have a duplicate signed card in their pocket from the start. They can react better than geniune people a the climax of a trick. With just a little acting skill in your part, you can basically create miracles. You can even do a whole show based on them. Be just like the pros, use the STOOGE 2.0 system."

Would make a fun viral video (but if you do, please credit me).