Shill (noun)

A person, especially a performer or employee of a carnival, who poses as a member of the audience and encourages others to participate or buy, typically in order to inflate attendance or sales.

Origin:

Of uncertain origin, it first appears in the early 18th century. it may be related to the low german schellen, "to make a noise," or to the yiddish shillen, "to beg.".

Examples:

1. The street performer had a shill in the crowd, pretending to be a member of the audience and encouraging others to participate.
2. He was a shill for the carnival, pretending to be a customer and encouraging others to buy tickets.
3. The shill was paid to inflate attendance and sales.
4. He was a shill for the casino, encouraging others to gamble.
5. The shill was pretending to be a customer, but was actually working for the store.