What they did was make posters for a film that didn’t exist. They brought out ads in papers, they surreptitously inserted trailers into people’s memories, interviews with a cast that had never been signed on. They paid a bunch of people fairly well for this, and these people were conscientious workers.
Then they sat back and gauged the response. They noted everything that people seemed to like about the trailer, the ads, the posters. They made a point to see what the people were most excited about.
Then they saw how many people came to a showing that never happened. They liked what they saw, especially the stone-throwing at the no-show.
So they went back in time and put the film into motion. They had the film written, scenes from the trailers integrated. They made sure every variable was the same, that every promotion was released on the same date, in the same places. They even managed to rope in the stars (it was only the expensive ones that ever made a fuss).
The film was released on the exact same date and everything. Big flop. Bummer all around.