Thoughts:
1. the OP has this "thing" he does where he endlessly asks some variation of the same handful of questions over and over again, all of the same theme. To whit, that somehow us producers force models to do things during shoots that they can't take and "have to" endure. I've confronted him on it in the past, but since he shits and splits (that is, never sticks around to engage in any of these brainless, low-effort threads once he posts them), it's basically pointless.
That said:
2. Sole_Scream's interpretation of the question is correct, based on OP's post history.
3. Yes, basically any producer with half a brain negotiates limits, activities, and what-not with the model ahead of time. It's not always as specific as checkboxes and a contract; none of the models I've ever worked with (fifty-plus and counting at this point) have done more than give a yea or nay to any of my proposed activities, usually between segments when the camera is off. "Hey, I want to try this position, you down?" "No, I don't think I can put my leg like that." "Ok, no problem."
4. People do in fact "spring" shit on models that they didn't agree to beforehand all the time. It's a spectrum; you may have said "this is a foot tickling shoot" and then reached up and given the model's knee a squeeze and gotten a good reaction so decided to focus there. The vast majority of models will tell you if you crossed a line in the moment, and they'll usually be good about it; "I'd rather just stick to the feet". "Ok".
Obviously, the issue then becomes whether or not the producer either pushes, tries to negotiate, or flat-out ignores the model's stated boundaries once given. This will get you in trouble. Models often have some kind of security; either they travel in pairs or bring a very large male person with FAFO tattooed on their knuckles to the shoot to disincentivize this sort of thing. It's usually all very friendly and does not involve the kind of autistic nitpicking this forum loves to engage in.
5. If you do screw up #4, if the model has any presence in the community she will tell others about you and recommend that they not work with you. The last thing you want is to develop a reputation as an unsafe producer who ignores/pushes stated boundaries.
5a. Obviously some transgressions are worse than others. Tickling a model under the arm when she only agreed to feet may get you a safeword and a "please don't touch me there", but whipping it out while they're tied up and insisting that you're going to shoot a footjob segment now when it was never even discussed beforehand might get you a blacklist or a beating.
6. Yes, and I've said this billions of times in the past; unless you were on-set you do not know what did or did not happen behind the scenes. This goes for all of the so-called accusations of fakery, but also shit like "wow she seemed really into it" or "she clearly said no, her boundaries were being violated". You weren't there. Keep your yap shut. Also, producers and models lie after the fact, often to "sell" a product - a lot of times they're playing a character. Take everything you hear with a grain of salt unless you're in the business yourself.
7. We do talk. If you develop that aforementioned reputation as unsafe, it will spread. There were at least two instances of creepy stalker people and nutty producers getting banned from conventions recently due to the chat from the mailing list I belong to. Producers who've been "at it" for a while. So don't think you'll get away with it. It'll catch up to you.
8. "Do people really believe XYZ?"
Yes. Yes they do. People in this community are, in fact, dumb enough to believe everything they see on YouTube. There's an unfortunate balance that needs to be struck between marketing fantasies that people want to see with dumbasses who think those fantasies are reality and that they can go harass women at the mall because some other dumbass did it, not knowing that said dumbass' videos are staged.
9. Happy Holidays.