Most of girls who attended to the party were came from agencies, they might get contracted/contacted and appear for few episodes , perhaps they will attend to the party and see how it works first and only get paid with free booze. If the money right, They will do as directed by the previous director, it is possible that some of them will be paid on the spot without being contacted first, I mean spontaneous.The girl from your link was kind of a regular for some time. She gets fucked in at least two episodes, does a blowjob in another. Even though she might be, strictly speaking, an amateur, I always had the impression that she was there for the money. I never had the impression she did it because she was in the mood for it.