Handing back a scored paper would probably be one of the ways I'd test for a written plagiarism. If the student gets mad at me and fights then they didn't plagiarizer. It's the presumed nature of humans to want to fight back when wrongly accused of something--even more so when you're found guilty of something. I'd accept a rebuttal saying that's not a correct model for every student and as such I'd find it evenly as "not-suspicious" if the person went to my boss or the dean and asked for them to get the points back.

If the student does nothing then I'd assume they did copy.

I'm sure people will be mad about these assumptions but from my experience--and from what I've seen my colleges fall into after wrongly accusing someone of cheating--I'd definitely say this is an appropriate average model. I'd also say it's lived to fruition in this case. The author got mad and wrote a fantastic expose on this situation. If I was the professor I'd correct what was obviously my mistake at this point.

In my view, the problem with using psychological manipulation tactics, is that it abuses the asymmetrical relationship between the teacher and the student. I think it would be more ethical for the teacher to simply lay their cards on the table. If they have evidence, present it directly, otherwise wait for another day.

The problem here is that you are effectively punishing students who have done nothing wrong. This is a great way to get an uncooperative class who don't really care about the work beyond the grade they get at the end.

Again, I've never caught a student who didn't admit to it. Those who have apologize and restore credit.

The student is usually happier to have that it seems since they get to say "I fought the law and the law didn't win" to their friends and classmates. The teacher does look like an idiot to the class after that though.

It may well come a time when I make the same mistake but at that point I'll be excited to admit I was wrong and restore credit. I'm not ashamed at failing myself, only know-it-all-do-nothings are afraid of ruining their street cred.