I don't see the point of telling someone they should be able to play something correctly - if they can't, they can't.
Indeed. No one tries to get it wrong. But maybe my teaching isn't hitting the spot, maybe the student has a persistent misperception that I am unable to shift.
I did have one adult student who eventually gave up. He would get very worked up about his mistakes, reprimanding himself, loudly, while he was playing. Both his sons had learned music to a high degree - one was an organist, one conducted a brass band. I could not get him to play anything at all with good tone, he just wouldn't play the notes properly.
Here's how it might go: I would ask him to play some notes, with detached tone, letting his arm weight depress the key deeply. He would reply that that's just bashing the keys. He wanted to do it lightly. He would tell me of recitals he attended, proud dad of talented kids that he was, and he would see other people's children just bashing the keys. But, I think in his mind, his children were better than all that. He had so many years of musical misperceptions built up in his mind and heart, that were so deeply entangled in his love for his sons. Nothing I did or said made any dent in him.
I think a lot of students are like that. They see someone playing Fur Elise well, and it looks like they're gliding over the keys. No, they're not gliding, it just looks like that. Actually they're playing with arm weight and good tone. Also, they learned deeply how to recover from a mistake, because they imbibe in the flow of the music.
So, no, I don't think that reprimanding anyone is appropriate or helpful. Now, if they forget to pay me, then that's another matter...