Which does not make tracking everyone a solution to the problem of cheating in exams.
Higher level education is largely voluntary, and it's up to the person taking it up to decide what they gain from it. If they are only in it for a diploma, they'd get there one way or another.
To me, focusing on finding "cheaters" makes education a competition. I never felt cheaters got anything over me in my studies, and I never felt like I've got a lesser grade because of them. Does that happen in cases where you've seen "exam-sitting-for-hire" in action?
Even if you normalize your grading scale based on the students taking the exam right then, if your claim that "most students are honest" is true (and I believe it is), that should not affect any non-cheater significantly (unless you've got a small, non-representative group, but then normalizing grades is unfair to begin with).
So my question is: who are we trying to solve the problem for? What is the expected outcome, knowing that there will always be people who "cheat" their way through life too?