When I see an actress in a nude scene I just figure she slept with the director, the producer, her agent.
I would bet almost every actress today has, at some point early in their career, had sex for a role.
Produces, casting directors, etc. wield an incredible amount of power. There are thousands upon thousands of young beautiful girls (and boys) who will do anything for that one big break.
And the actress who won't put out for a role? Well, there's a whole bunch in line behind her who will.
Running a casting couch was pretty much what Bill Cosby was doing, except he wasn't making good on his end of the deal.