Do you really think professors flag plagiarism only when it's cut and dry? Absolutely not. Plenty, if not most, flagged cases of plagiarism are ambiguous. The process at most colleges and universities typically accounts for this via something like review by an academic integrity committee.
Agree. I was accused twice of plagiarism by professors in college. Needless to say there was zero plagiarism involved. In both cases I wrote code that they didn't think it was likely that an Nth year college student would know how to write. In both cases it didn't go anywhere. One because they talked to me about the work and it was clear I knew my stuff, the second because the professor was certain I had cheated somehow but couldn't prove anything despite his attempts to find the code he insisted I must have found online. I'd say the existing process is already higher than 1/10000 false positive!
