Yes, that would be terribly off-putting. If it was my mistake, I’d suck it up and eat the hours, as I think that would be the professional thing to do, which hopefully would preserve the relationship. But the to-not-exceed quote, and the a la carte menu, is supposed to prevent uncomfortable situations like those.
I’m fortunate to not rely on client work for my bread-and-butter however so I could be hopelessly naive.