Notes on Fair Use (Warning: this may be a copyright infringement)

When I first began to read the article about a company that sells bundles of notes taken from a professor's class and books, my immediate thought was that that was wrong, it was clearly a copyright infringement. But then, the article drew attention to the fact that if doing so was a copyright infringement, then a student taking down notes in class and long-standing companies such as CliffNotes would also be in murky water - things that don't seem like copyright infringement to me necessarily. So that's when I realized that what I felt was really wrong with buying notes from a company was that it was an ethical infringement more so than a copyright infringement. But, ethics aside and sticking the the lay of the law, I would say that selling notes taken from a professor's class is not a copyright infringement. However, I am no law expert and this whole issue of "fair use" seems to me to be a very gray area. I propose this instead, how about we avoid this whole (very) gray and messy situation by letting professors who want their work "protected" have all potential students sign a waiver saying that they will not sell their notes for profit. That way, there were be a legally binding contract between the professor and the student so both know what they are getting into.