ROXIE: Don't you think it's about time that I met your friend down at the Onyx?
Fred later mentions that he was only telling Roxie he could hook her up with a manager in order to hook up with her… but what if we turned the tables? Is Roxie interested in Fred for himself, or because he might be able to make her famous? Who's more manipulative in this situation?
ROXIE: And, you know, it occurred to me the other day that all the really, really knockout acts have, you know, something a little different goin' on, you know? Like, um, a signature bit. […] And I thought that my thing could be aloof, you know. Give 'em just enough to get 'em good an hungry, but always leave 'em wantin' more.
This is Roxie's key to showbiz and, really, to life. It's a way of manipulating a crowd even if the crowd is the general public and not an audience watching her on stage.
MAMA: I love them all and all of them love me, because the system works, the system called reciprocity! […] Got a little motto, always seen me through, when you're good to mama, mama's good to you.
Mama is a master manipulator, and she knows how to game the system, but in order to play the game, prisoners have to convince Mama that they're worth it.
MAMA: Baby, you couldn't buy that kind of publicity.
This is ironic on Mama's part, because if there's anything Mama knows, it's that the best way to manipulate someone is with cold, hard cash.
MAMA: The truth? […] That's a one-way ticket to the death house.
Mama makes a good point here. The truth is boring. The public—and the courts of Chicago—want a show. They want to be entertained.
VELMA: I can't remember a thing. Only that I didn't do it.
Velma is very good at manipulating reporters and maintaining her innocence. She has to walk the line between fame in the papers and not incriminating herself in the courtroom.
BILLY: You know, you're a remarkable man. […] Your wife two-times you, plugs the guy, then tries to pin it on you. Most men would let a dame like that swing. But, no, you're sticking by her. Makes you a hero in my eyes.
Manipulating Amos is like convincing Jessica Simpson that Chicken of the Sea is chicken, but Billy doesn't only pick easy targets. He knows how to work everyone.
BILLY: Nobody's gonna care a lick what your defense is unless they care about you. First thing we gotta do is work up some sympathy from the press. [...]But here's one thing they can never resist, and that is a reformed sinner.
Continuing from the last quote, we see that Amos was just the warm-up act. Billy's target is the judge, the jury, the press, the public. Basically everyone.