These two are the two bigger ones, but there are others.
Actually, I use these guys as research material. If I see a good-looking plan up for sale by them, I then do some digging around on the magazine websites (RCM, MAN, FM, Traplet, Nexus are my usual choices) until I find the plan.
I then order from the publisher simply because I know that the plans are going to be good, I'm supporting honest publishers, and often you get a copy of the original construction article.
Yes, I do sell my old plans on eBay but I don't flog copy upon copy upon copy...
When I was doing a corporate logo, I checked with a copyright lawyer on what the situation was (this is 15 years ago so it should be close-to-current for Canada and the US at the least.)
Unless you have made substantial changes to the original, all you have made is a copy not a new creation that can be protected by copyright. Removing water marks, tears, stains, and refixing lines does not alter the drawing enough.
If you take the original drawing and then update the cosntruction techniques and internal structure (eg, coverting a IC engine to an electric motor and lightening the bulkheads and shifting the wings and stab around a bit for better performance), then it can be classified as a new creation.
I did notice that SS01 is selling CD-ROMS of plans. Big clue that he has no respect for his sources and buyers. I once picked up someone else's (dirtriderdude) and everything was scanned from magazines. Poorly at that.