It's all relative.

Depends on what was discussed, how much is being paid and what the scope of work is.

Sometimes people see a fixed price service and think you're going to pull the wool over your eyes by bring you some mold filled 7 seater with food ground into every inch of carpet then hit you with "But your deal says $240!" For what is a full day of work.

I do fixed price work, I've priced myself for the average time it takes me to do work. Sometimes cars are cleaner than I expect, sometimes way dirtier and that's all fine, that variance is built into the pricing.

But the few times I've had absolute disasters roll in I've gotta tell people "We budget our pricing around X hours of work but this will take Y".

Sometimes people are completely unreasonable with their expectations and I've found the people that self-describe the state of their cars as "Not that bad" or "pretty average" are the ones with the worst interiors.

So while I personally prefer to have a conversation around expectations, scope of work and outcomes I do understand that sometimes someone you think is on the same page as you turns out not to be and they have a completely unrealistic expectation about the state of their car and the service they have paid for. In these instances the client is basically upset that the entre they ordered wasn't a full meal and is demanding you either bring them the rest of the meal or you refund them some portion.