It could also be blackmail... remember, in order to became a HOT, girls need to complete several tasks which include handjob, blowjob, sex in public (or is it just outdoors?) and they need to provide evidence of the act. I wouldn't put it past Quinn to use that evidence to blackmail someone into joining her operation.Which means that if Quinn managed to win so many over to her side, there was some convincing involved.
That said, none of the girls currently involved with her prostitution ring look like they're blackmailed into doing it but that doesn't mean Quinn wouldn't use blackmail if she consider it necessary...