There is an easy solution to this. No reason Jon can't create an "open source" license that forbids anyone from making money off the project. Heck, he could even just copyright his site if he wanted. It could be as simple as a couple lines at the beginning of the thread or category. Most outfits like eBay don't want the headache so simply reporting that the material is copyrighted would most likely be enough.
I once bought a PDF on eBay that was called "Hanger Door Secrets" and was advertised as having plans and material for several different types of hanger doors that you could DIY. It came with a 100% money back guarantee. Turned out to be a few paragraphs and a bunch of links to various websites with no original information in addition to pictures and info stolen directly from those websites. The guy wasn't too happy when I told him I wanted my money back and that he should be ashamed of running such a scam. In the end he gave me back my money at least.
