money and degree of responsibility

Does obligation increase with increase in payment? That might not be the best way to formulate the question--it's a bit too abstract as it stands, but here goes....

Last week I was discussing a student with one of my supervisors, and at the close of the conversation I was given the following as a parting shot,.....
(something like this)
And since the student's parents pay so much in tuition we really owe it to them.....

The question which occurred to me was something like this: does my degree of responsiblity/obligation increase as tuition increases? or, isn't it the case that my obligation would be the same if I were doing volunteer and for-free teaching?

I mean that I've promised to teach this student and I represent myself to the world as someone who is able to do so, and therein lies the ground of my responsibility--not in the tuition paid by the parents.

Put differently, if I were teaching in a school attended by poor children, would my obligation be less?

It is true that I found the comment bothering, and, also distasteful. The amount of money paid is an indication of the family's standing in the society, their social class. It is not an indicator of virtue earned. In other words, the students come from privileged backgrounds, and, due to that fact, I actually think my real responsibility is somewhat less. If it every actually happened that I didn't on a given day do a good job, these kids have so many advantages, that they won't suffer greatly. NOte well, that was a contrary-to-fact or imaginary conditional. I am not proposing to slack off because these kids are privileged....

Final thought; to be sure, were large sums of money are involved, there may be obligations incurred. I"m thinking of someone's life savings. But that seems to be a different case.
(And if a parent's life savings is spent on education for a child? Right, that would increase my obligation. but so far as I know, that's not what we're talking about in this very particular case....)