I like your movie screening example.
Let's say you want to watch a movie about a certain topic. You ask a couple of friends if they can recommend one. They respond by telling you about this free movie screening at the local park - the movie is exactly about the thing you're interested in. You go to the park. Five minutes into the movie they start asking for money or you have to leave.
- I think your friends might not have recommended the movie if it wasn't free
- you might not have gone to the movie if it wasn't free
- nothing on the outside of the movie screening area indicated that they switched to a paid screening
I feel like there is a difference between a free screening to get some publicity and a simple bait and switch.