I am usually someone who is a really, really nice person. However, the answer to the above question is a polite no. (There are ways to say it, though.)
Reason: You can afford my services but you cannot afford the payment?
I believe that’s not the case.
It is simply the human nature of deferring payments as much as you can.
Love your clients. Go the extra mile for them. But know that no one is coming to save you, unless you draw boundaries of what is important and what is not important.
You can stand for yourself and be a nice person. They aren’t mutually exclusive.