In my experience about 9-15% of people will, if given the chance (Freedom), screw the system. When you have a Dictator then about 8% will figure out the new rules of the game and try to screw the system. I know, because I am a Dictator, of a sorts
It is the ONLY means of accomplishing what I do - Lecturing
I have found that when I am easy I have a HUGE number of Deferred Exams 12%. When I hammer them with a Wall (AKA: A mess of paperwork and threats...) still 5% will figure it out *Grrr*
So what I do is have the Deferred 1st test
after the test 2 during the same day and period. Haaa! I STILL had one student try to take the deferred AND pretend they were too sick to take the preceding test-2!! Which THEN I can finally call BS on the Medical Certificate and not worry about slander
If you are good to take the deferred then you are good to take the test2...