Paid to watch

When audience shots are a necessary part of the show but the show isn't hot enough to fill all the seats, people are paid to be part of the audience. Via this Animal account of an American Gladiator taping:

And yeah, being an audience member is as phony as the rest of the show; its a paying gig! A steady thing gangbangers, failed actors, those to dull witted to hold down a security guard gig. And the American Gladiator producers never let these marginal types forget they are the lowest of the low. They're kept for hours on end with no water, rousted out of toilets and not compensated for a lunch hour. One sad sack who relies on "audience work" for a living said he considered complaining to the NBC over his treatment that day, didn't have the cajones. "I don't want to be black balled from this work."