In my college days, I did night service on Jukeboxes and, although the slug rejectors in those days were purely mechanical, I gained a lot of experience with what individuals would do to defeat the mechanism.
If your project is for something that has no real value (e.g. a stolen song from a jukebox) go ahead and make your slug rejector; however if you are talking e.g. cigarettes, you are up aginst the most devious minds in the universe and Andy is right it is no simple task.

Erik