[ye]

> But adding this as a requirement is perfectly reasonable?

If you don't think it's reasonable, why agree to the project?

> Next time I buy some bananas at the supermarket, I'm going to tell the cashier that if my clients don't like them, they won't get paid

That's a red herring fallacy, it has nothing to do with the situation we're discussing. The cashier has no contract with you, and didn't agree to anything.