There was a guy a few years back who tried to corner the market on a certain used camera, claiming that it was obsolete and could only be made useful with a modification that he patented, and then he sold his modified cameras at very high prices. Let's not mention his name or get into a discussion of that guy, who seems to have faded away, but Camera Rescuers don't seem like that guy.
If they're a dealer, then they're competing with other more established dealers who are using a similar business model--buying cheap gear however they can get it, fixing what's good, and selling it for a profit.