The Trailer checks through Movie Measure are very easy to do. You don't make a lot of money doing these, but people who can secure more than one location can make a day out of this on a Friday. The more locations you can get done, the more money you make. No, you can't stay to watch the movie you are checking unless you buy a ticket for that movie.
I have been doing trailer checks for other companies before Movie Measure even existed at my local theaters, so I don't have a problem with management, crew, or anyone. You do leave the auditorium once the trailers have ended and you finish entering the data in your app in the lobby or hallway, wherever you choose.
Most theaters have cut down on the number of trailers they play now, so even if you're just not that into trailers, it's still easy money. Especially if you have nothing else going on on a Friday, and you need an extra few dollars.
I don't know of many shops that pay a ton of money anyway, but for the past few years, I have switched to strictly theater work and only theater work. So I may be out of the loop on high-paying Mystery shops. As the other poster mentioned, they do have installs, Open checks, and at select locations lobby checks.
Trailer checks just happen to be the type of assignment they get most frequently.