Here's a winning formula:
Hire a cute, naive, ambitious newbie. Treat her with professional courtesy prior to shoot. During shoot, degrade the bitch as much as possible without leaving yourself & your crew open to criminal charges. Pay the dumb whore, hire the next, and keep the juggernaut rolling along. The heat of scenes carried out like this is scorching. Really erotic stuff. Particularly that surprised and disgusted look on the dumb whore's face throughout.
Hope this helps.