Claquing reportedly emerged in the 1820's as the idea of French businessmen Sauton and Porcher. The owners of opera houses in Paris would hire them to applaud enthusiastically (claque) and, through the principle of social proof, guarantee a pleased audience. They organized a company called L'Assurance des Succes Dramatiques that offered applause services for theaters and operas. Claquing became a very effective method of increasing audience enthusiasm.

The practice of claquing soon became commonplace in opera houses and theaters, and little effort was made to conceal what they were doing from the opera-going public. The practice has even made its way into modern times through the use of canned laughter and laugh tracks on some television shows.

Different specialties arose within the world of claquing as well:

chef de claque: the "claque leader" pleureuse: the claquer who would weep on cue
bisseur: called out "Bis" (repeat) and "encore"
rieur: the claquer with a particularly infectious quality in his laugh.

A company called the Italian Claquers put the following advertisement into the Musical Times newspaper, advertising their rates for claquers:


For applause on entrance, if a gentleman 25 lire
For applause on entrance, if a lady 15 lire
Ordinary applause during performance, each 10 lire
Insistent applause during performance, each 15 lire
Still more insistent applause 17 lire
For interruptions with "Bene!" or "Bravo!" 5 lire
For a "Bis" at any cost 50 lire
Wild enthusiasm--A special sum to be arranged

Influence: The Psychology of Persuasion by Robert Cialdini
http://www1.appstate.edu/~beckhp/socialproofopera.htm