After some consideration, I decided that all "Guests" should use an open isolated VLAN, that only connects to the Internet. Isolated means that Guests are also protected from each other. For the rest of it I really don't want to know, it can only lead to "complications". Personally, I do not connect to public WiFis that try and harvest information about users (they get the MAC, or think they do).
Other WIFi users may connect to an appropriate SSID for the local/remote access that user is entitled to. Allowing staff some form of Guest/Public access only encourages them to waste time on social media sites when they should be working.
There is nothing to stop genuine guests connecting to the Internet using their MNO service. Staff may be required to leave their personal phones in their locker when working. This isn't necessary in most businesses, but hotels, bars and restaurants tend to have a problem. When I lived abroad, my cleaning-lady (from a former Eastern Bloc nation) used my apartment's WiFi to run an Escort service.