I think one thing I can't protect against is students completely faking their identities. Meaning if I expect Matt Smith, and Matt Smith has hired John Doe to interact with me all semester, I can't detect that, because I don't really know who Matt Smith is. But Matt Smith would have to know that John Doe will be available to impersonate him for the next 3 years because they will be taking several courses with me. If Matt Smith is rich enough to hire a double to essentially go through college for him, then good on Matt Smith for being independently wealthy I guess.

The other thing I do is I don't make exams so weighty. If you ace the exam but you don't do well on the assignments, you're not getting an A in the course. So the hypothetical wealthy cheater will have to keep their body double on retainer for the semester.

But I will say that the students who earn an "A" are ones I interact with fairly regularly. "A" students typically come to class, ask questions, engage with the assignments, start their assignments early, etc. And before anyone accuses me of playing favorites, I don't do any grading, and grading is anonymized. But I can easily predict the "A" students just by their work ethic. The idea of the brilliant student who doesn't come to class and effortlessly breezes through the exam is as far as I can tell after teaching thousands of students a myth. At least at my university. Maybe all of those kids go to MIT.