a lot depends on who books your work.
I had a girl show up to do a bondage set with me last week and her agent had not told her a thing! she had no idea how much she was being paid or why she was there! info her agent knew!
my agent tells me who I am working for, and who im working with, then they check the other talents tests for me and they tell me what im doing and what I will be paid, they give me a call time and make up artist info and what clothes to bring. if something "extra" comes up i get more money or i can call the agency and let them handle it. I never have to do anything that wasnt previously agreed on. (although being the uber whore I am I am normally game for more)
Producers will often try to sneak shit in on you, like "So how bout we do a double vag while your here"(hehe I snuck a double vag in on GBS hahaha I felt so bad for marcos) but it's up to you if you do it.
misscommunications do sometimes happen.But if you have a good agent it shouldn't be a issue, and if you book your own work, you find it all out for yourself before you arrive.
you get a feel for how long most shooters take, example, you work for adam and eve you will be there 12 hours you shoot a jm gag factor you can be in and out in an hour.
i love shooting for pussyman cause he shoots soft and hard with 2 cameras at the same time! mmmmmmmmm fast shoot