So change the wifi password.
You can even prepare for it by printing the details + qrcode beforehand.
Connecting to a wifi network is one of those things every terminally connected non tech savy people are able to do these days.
Not "my network has a default or empty password, I can't make people sign in again."
Also, some people have a lot of wifi connected devices, including stuff like light bulbs. (Again, not me.)