Well, @Brian658, that's the million dollar question that hosts on this forum have been asking endlessly. If you figure it out, please let us know.
As far as your specific problem, most people these days expect to be "connected". Even if you are clear in your description, they don't read, they assume. Each host has different problems with guest comprehension, and some the same, depending on the listing. In my case, I need to make sure that guests understand that while I do have an internet connection, it's metered and limited, not suitable for those who need to work online, or want to stream movies, etc, but fine for checking their email and surfing the net a bit. I also need to make sure they are clear that altho I'm in a beach town, I live in the countryside and it's a 20 minute walk into town and the beach.
So what you can do is, when you get an Inquiry, or a booking request, message the guest with a greeting and ask them if they thoroughly read through your listing, and are aware that there is NO WIFI AT ALL available. Make sure they acknowledge and agree before accepting their booking. If there's a cafe or somewhere where they can get Wifi down the road, make sure you mention that.