When I was young, I was a member of a modern church. One day I had use of a room, but it was already occupied, so I listened by the door to hear if it was an activity which could be interrupted.
In the narrow room (the door was ajar and I could see the occupants, people I knew) were two people sitting closest to the door. On the other side of the desk was a man being interviewed, if that's the word.
That man said: "Am I really being held captured here, like a monkey in a cage?"
One of his two interviewers said: "Have you ever had an agreement with us?"
All in all, it was clear that the guy was in the process of leaving the organization in some way, and that these guys were applying all the psychological pressure at their demand to hold him/get him back.
Now, only on vague rumor lines have I heard of people actually being held back physically against their will in this organization. I can't be sure if, when, or how often that has happened.
But I have heard of many, many people, myself included a couple of times, who were in interviews for recruitment or sales pitches, who were there long after they wanted to leave, and did not feel they could leave.
Now if I got in that situation today (I wouldn't, I know the type too well now, if there's no clear benefit to yourself, don't go), I would lean forward so the interviewer(s) knew to listen, and then I'd say something like: "Listen, and please consider the legal implications of what you answer to this: am I free to go right now?"
Any interviewer with a modicum of intelligence would know, or at least feel, that he would be in trouble with the law if he held you back by physical force or a locked door. And even if he couldn't answer anything reasonable, he would remain passive while you picked up your coat and calmly walked out the door.
And in the rare case when somebody might be stupid enough to actually restrain you, you'd just have to wait til the time you were free (sit in the corner and sleep or such), and then go to the police. In any Western country I know of, restraining the freedom of a sane adult, even briefly, is very much against the law. (In hospitals they won't even hold back a patient even if they know that he is highly likely to hurt himself by getting up.)
The only problem is that such interviewers are often highly willful people who think they have 100% of the Right on their side, and they have much to lose with their superiors, so they are very convincing. And most of the rest of us are simple generally timid, we don't want to make trouble or enemies, so we back down, maybe just arguing a bit.