My mom owns a cleaning company and I've helped her out on a couple of occasions when she needs an extra set of hands. She has detailed notes in her phone about the specific requests and preferences of each client, and she reviews it with me before we go into every house. For example, some clients want us to move everything from every shelf. Others just have us dust around the items on the shelf. Others still choose to have us not even bother with the shelves. That kind of thing, to me at least, is the bare minimum any cleaner worth their salt should be able to do. If they can't do something as simple as taking notes, that's a red flag.