Sigh. I don't like it when students sell their notes, but it's not because I believe I have copyright over their notes. But they are making money off of my intellectual work, which I do reserve the right to (i.e., I reserve the right to my lectures, not their notes). But I would never try to sue them or throw a fit about it. I'd probably just go ahead and put them out on a public website so that everyone could access them for free instead.