re: Asking to see a bill from a family member

Tell said family member that in the corporate world, some firms will reimburse you (that's after the semester is over, not ahead of time) but only if you get a B or higher. And you have to submit proof that you paid the amount you said you did.

If you have the money you set the rules. Not the recipient. I would, however, make sure those rules are clear beforehand. Afterward is a bit difficult. If that's the case I would say something like "OK - this time. But it changes from now on. If you don't like it, pay the bill yourself."