Residential: You can explain all day. They still (most) don't get it.
Explain some more- or just do the work.

I draw the line with I may need to make a whole here or there.
4" hole saw and replace the piece.
After they see the sweat and occasional curse word.... Not an issue with the time or the bill.

Commercial: 'I want this'. Ok.

"Your killing me Kid!!!, But here's your money".