Although I am not sure the scenarios TimR describes are accurate of what actually happened, there are some very good points (I certainly will keep them in mind for future reference) in both his posts

(even if they are irrelevant for the problem in question).
I do agree that expectations from both teacher, parents, and perhaps most importantly the student must be somehow reconciled.
The problem is that expectations can be so off the mark that sometimes it may be better to ignore expectations completely, plunge ahead and after a while reconsider them again on the light of the experience of what it really means to learn the piano.
What about these expectations:
1. “I will buy a piano once I know Johnny really wants to play”.
2. “Johnny will start practising once he is at the advanced level”
3. “Right now Johnny is under a lot of pressure in school. He cannot really play the piano outside lessons.”
4. “Johnny does not want to play classical or read music. All he wants to do is to be able to play songs that people ask him to play. Can’t you teach him just that?”
5. “I am afraid Johnny will not be able to come to lessons or to practise for the next six weeks since we are on holidays. I know his exam is in eight weeks time, but you can give him some extra lessons when we come back, can’t you?”
6. “ You are not teaching me anything.” (Johnny who never practises or go near a piano besides the lessons).
7. “You never taught me that” (Johnny, who is then shown an article I gave him, went through the article with him in several lessons. The article has the information he claims was never given repeated several times).
But perhaps the best story is the one about the teacher who taught a student for free (the parents claimed to be in dire straits), and succeeded in bringing the little Mozart from knowing nothing to passing his grade 3 in less than a year. The mother then informed the teacher: “Now that Johnny has learned the basics it is time for him to have a real teacher”, and promptly moved the prodigy to a paid teacher.
Or this nice story (not a piano teacher story). This lady was trying to learn English and not getting anywhere with an English teacher who she claimed not to be able to afford – and in any case she was not really learning anything – or so she claimed. My wife, who is a qualified English teacher, took pity on her and prepared her for free for the Cambridge First certificate examination. For over seven months she gave this lady daily one-hour lessons, with videos, exercises, lots of preparation and so on. It was really hard work, since the lady in question was how, shall I put it, on the side of intellectually challenged. The lady took her exam and passed with flying colours. After the exam she came to my wife and made the following request:
“Can I ask you to keep a secret? Do not tell anyone you gave me lessons, because I went to the house of my former teacher to tell her I passed the exam and thanked her for her efforts and gave her a nice bottle of wine, so she now believes that it was thanks to her that I passed, and I don’t want to hurt her feelings.”
Nice, heh? (By the way, my wife did not even get a “thank you”, although I was more interested in the bottle of wine

).
So, although I like your compassionate approach, I also think that each case is each case, and if you let, people will always take you for a ride, and it is really your fault if they do.
Best wishes,
Bernhard.