What has always amazed me in the crux film field is acquiring the models. How do you find beautiful young (and sometimes innocent in this case) young models to agree to be crucified and photographed nude and to experience the pain and discomfort that entails? That is the true artistry of the genre. I know several have porn backgrounds, but even if they do, it must be pretty extreme. Even an experienced nude or erotic photographic model must be given pause.
I know several of the producers would simply introduce themselves as art photographers and be honest up front: "You're beautiful and I'd love to photograph you. Here's what I'm thinking..." and then explain the pose and the bondage. John Blakemore was a producer who sold to HOM and Lyndon magazines in the 70's and found most of his models working as waitresses or walking around in public. He simply walked up to them and told him what he wanted. He got a lot of rejection, but he only needed a handful of women who understood his art in order to produce an impressive collection of work, and those women found pretty steady work to supplement their day jobs.
Another studio would advertise on college campuses, looking for amateurs willing to test themselves and their own limits. Respondents would come in for a camera test, be given a few licks or spanks to see how the skin reacted, and arrangements would be made for a bigger shoot. This way still works for simple shoots, but is risky if the model has a change of heart down the road.
Times changed for more elaborate stuff and it became easier to just work through a model agency. If a model complained about the producer, the agency would stop sending models. If a model said one thing, but then backed out on the day of the shoot, the producer would complain to the agency and the agency would drop the model. So, there was a system of checks and balances through a third party. Don't want the work? Ok, bye. No hard feelings; its just business.
The rise of social media has created new opportunities for modeling, but also made things difficult for producers because OnlyFans and similar sites allow models to be their own producers and put content up for sale for themselves, of themselves. The real value for producers now are equipment, props, and photographic skill. For Alex, I would imagine it is the availability of his equipment and how he treats his models (very well). The models control the shoots and can call "Camera Stop" if things get too rough.
I think for the most part, the women are motivated by money first, and then by their own curiosity second. But I'm not a model so I can't say for certain.
I can tell you that when I have a script I want done, I zero in on models without obvious tattoos who can look far more innocent than they really are. If I learn that a particular model is a college student, I try to book her first, for as many scripts as I can, before she graduates and moves "into the Real World". The reason is that in college, a girl isn't producing income sitting in a classroom, so her finances are thinner. After college, she becomes a wage earner, so the financial motivation isn't as strong. And that's when she gets a serious boyfriend and has to either confess her side job to him or drop modeling and focus on her relationship. So there is an urgency there if I want a particular college girl for a particular script. There are only a handful of Alex's models that I can count on to be available this year as much as next.