Do you know the complaints developers have about their clients not having a clear vision and constantly changing the project requirements? That's them crying over their own inability. Whenever I hear this, I wish the poor client had a better provider.
The client doesn't have a clear brief because they are not experts in web design. I wonder how many web designers understand their client's business well enough that they could create a precise brief if the roles were reversed.
If the client continuously changes the requirements, it means they are interested and engaged in the project, constantly thinking about it. There's a higher chance that something truly useful will emerge. And most importantly: they will keep asking for more and more work.
If the developer realizes this, they will understand that it is they who must adapt their working style. Perhaps simplify the addition of a ZIP code column on the website, even though it wasn't in the original brief.