I had a player many years ago, early first edition D&D, who went out and bought the module I was running. He was playing in a very focused way, unusual for a normally chaotic player. The rest of the group liked the fact that he was not setting off traps and attracting wandering monsters, none of us realized he was cheating. The Macguffin in this module was a super powerful sword that was way over powered, so I had rewritten the sword to give it some negatives. He wound up getting the sword, of course as he was laser focused on it.
Well over the next few months he became very agitated every time he used the sword’s ancillary powers, some bad stuff would happen. Finally in a fit of pique he yelled “That’s not right, I have the module and you are not playing the sword properly!” As he looked up at the rest of the table’s horrified looks, he tried to back pedal. Well, somebody at the table, not me, dumped his bag out onto the table. In it were not only several modules we had played or were looking to play, but xeroxes of my notes! I worked at the same place and would bring my bag of DM stuff to work and we would play after work.
Needless to say, that was his last game at my table and the last time I ran a module. I continued to read them for ideas, but wrote every single adventure I ran. Forty years later I still create all of my own material.