There comes a time in every music teacher's life, that he/she finds himself completely fed up with a certain student.

I had a guitar student who wanted me to teach him twice a week, for 50$ a lesson. A 12 year old boy from my city.
An extra 100$ a week (400$ a month mind you) was a VERY nice addition to my musical income.

After an ongoing while of this "too goo to be true" story, I found out that the student lacked in musical abilities, and a desire to practice.
In fact, he seemed to be making absolutely no progress between one lesson to another, and I found myself counting the minutes until the lesson was over.

At the end of the day, I had enough other students, and the anguish of sitting through the fifth lesson where we play the exact same Greenday song, with the exact same errors that he didn't bother practicing, were not worth it. I graciously explained to his parents, and got out of there.

I think you really want to be the kind of teacher who can afford to take only students that interest him, and that are fun to teach.
We create our desired future by our actions today. If we allow ourselves to get stuck with boring, unmotivated students who will suck the teaching energy out of us (That is well deserved to our other students, and it's a waste!)we allow this element to exist in our lives and it will continue to appear.