I love the store Chumleighs, which sells used games and movies for great prices. A few months ago I was thrilled to find a Playstation 2 game I'd been looking for for a long time: Hulk: Ultimate Destruction, which had been very well reviewed.
Unfortunately, the game did not work. I cleaned it and tried several times, to no avail. I planned to bring it back. And even though I had no reason to suspect Chumleighs of any foul play, just to make sure I never bought that particular disc again I put a tiny dot of ink on the case insert in a place I would remember later. They gave me my money back.
Just today I was browsing, and there was the Hulk game. With the same dot. I told the clerk that I'd returned this game and was disappointed that it was back on the shelf. She said that it might be a different copy, and I told her about the dot. She took the game to the back, and discussed something with somebody, and then put it back on the shelf, right in front of me.
Pictured: Graffiti. From Wikimedia Commons