I’ve been reading Robert Cialdini’s "Influence: the Psychology of Persuasion" (good book, by the way) and at one point he discusses how the claqueurs would charge to clap at appropriate points during an opera. They even published rates for clapping: applause on entrance cost 25 lire for men and 15 lire for ladies, "ordinary" applause was 10 lire per, "insistent" applause cost 15 lire, and "wild enthusiasm" cost "a special sum to be arranged".

Pull open a Sunday Washington Post and look at the help wanted ads for a reverse phenomenon: ads for protesters. Those paying for protesters to show up to an event must be aware of the phenomenon that Cialdini refers to in his book as "Social Proof".