In my experience they turn up for the money, on casting and on shoots.
Nymphomaniacs have no problem getting sex, exhibitionist can get seen far easier than doing a shoot and any girl who wants to be a porn star either wants to do it for the money or should be kicked out the door.
Yes a few ugly ones might want to do it because it would mean they could do it, but I never let them get that far. I politely tell them they're not what I'm looking for at the moment and send them home. Some offer me sex in return for money, as they need the money.
Girls who need the money and know if they don't perform to the shooters needs or will go home without any money are the greatest. They're easy to control. The shooter has to do it in a gentle fun way to make sure she works with a good heart.
And that's the key, good positive communication with a model is the paramount importance. There are different ways to achieve it.
Firstly on the interview. Good greeting, smile confident handshake and say something nice about her shoes or clothes or hair.
Be in gentle command, lead the interview as a person who has done this 100s of times and still enjoys it. Ask her if she's comfortable doing this, if she says no withdraw and let her go. No force. She will probably change her mind and it puts you in command.
Letting a girl see that you have professional equipment as well is positive.
On the shoot know exactly what you're doing. What you need her to do and how you want her to do it. No times for questions except "All Right?" in an assumptive manner.
All this has to be delivered in a fun way. Being able to assess who she is and her character is good. Girls who give me the impression they think I want to jump into bed with them, I tell "There's no film in the camera and I only do this to see naked women." Said with a smile it disarms mosts girls. Even today when there's no film.
An over confident girls needs bringing down a bit. An under confident girl needs building up.
The bottom line is always the money and it's good because it controls the girls.
You just have to be sweet and nice about it, without giving her the idea you're hitting on her.