As far as I know, I don't have competition where I live, but then again, there really aren't too many places too hunt. With that in mind, I would understand having a bit of a rivalry with other people that are also hunting for games, and not telling them where you're getting your stuff from. But even then, it's a matter of time until they find out, and more often than not it tends to be sooner than later. In the end, that kind of behavior truly is an exercise in futility. But to each their own, as they say.
This mentality can also be seen on some YouTubers. In one of his "breaking the seal" videos Radical Reggie mentioned having bought the game he opened online, but that he wouldn't reveal where because he still wanted to get more stuff from there, implying he didn't want others to potentially buy whatever he wanted. I tried to find the video in question, but after watching two or three I just couldn't be bothered anymore. I don't remember the game that he opened, but I recognized that he had bought it from an online retailer called GameQuestDirect, known as dealtavern on eBay and Amazon.