I'm also a teacher (music) and do run into the same problem on occasion.
It seems to be a generation thing - people these days seem to be better at making excuses than improving at a skill or trade. I don't know what to say, other than we do need a strategy.
I would support you if you chose to drop students that don't want to listen to any instruction (why should they waste their time and yours?)
So I'm a chess coach.
I tell all of my students to win and lose graciously.
I primarily target students under 1400 (I won't coach anyone that is within 300 rating points of me). I coach for free and I do it because I love the game. I'm used to the typical problems of students (wanting rapid improvement, not listening to your coaches opening recommendations, rivalries etc... bad habits die hard).
However, I've picked up a few students as of late with problems that I've never experienced before: Modesty.
Example, I have one student that plays over the board and starts to boast or talk loudly when he has won the game against a higher rated player (or near proximity)... I've tried telling him this is bad chess etiqutte, but he keeps repeating them same thing.
I have another student that DRASTICALLY overestimates his strength because he has drawn a higher rated player. I've beaten a FM master in blitz and one in correspondence, but that doesn't mean I am the same strength as them! Maybe it means that everyone can make mistakes! It just seems that this may be a character flaw that's bigger than chess and I'm not sure how to handle it.
Another one
There is another that blames every loss on anything but his play. A typical excuse would be, "If only I wouldn't have dropped my queen ...he was lucky," or "I just do bad against 1. e4!"
Just want to hear your feedback. I feel the students have potential, but to be honest, it makes me not want to coach them. Especially the older ones. What do you think?
Even Veselin Topalov, the world's highest rated player is humble.
http://www.youtube.com/watch?v=1_W3NF4CEqI