This was fascinating as I was reading about how an instructor at a school was teaching a course on how to essentially run a film set with actors and these students pay a lot of money for their education. It appeared though that the teacher needed to find actors and therefore was posting various ads that he is looking for to volunteer where it should be about an eight-hour day.
Now in many cases one would probably get a lot of responses which encourages people to try and find free help. But in this case his ads were being criticized immediately as people within the industry started to express how that sounded wrong because the actor would be a part of the course essentially and so they should be paid just like everyone else.
Shortly after the person deleted their ad and replaced it with a new one where they would be offering compensation. It gives you the perspective where if everyone in a particular industry went against a practice like that then people will change quickly. It can be tricky of course if you are someone who really needs say the opportunity for whatever reason. But in the end it may work out better overall by not being taken advantage of.