Aren't Bad Auditions Faked?

Somebody clue me in. I don't watch American Idol, but give it credit for launching the careers of some talented people (like Golden Globe winner Jennifer Hudson of Dreamgirls). My questions: 1) how do they know that some of the auditioners aren't deliberately performing poorly as an act, just to make people laugh and to get on tv? 2) why don't friends and family discourage the talentless from auditioning?