I am not a spa owner or promoter and I have no skin in this game.
I am sure you have been VERY open with the owners, but bear in mind many (most) of them do not have English as their first language. They might not comprehend the guidelines that well.
I have no idea how you can communicate better with them.
If this crackdown is to succeed, you would also have to look at multiple handles which can or will be used to circumvent your action. When you cast a wide net like this, some those of that are, through ignorance (which is not an excuse in itself) get caught up in it.
But, some spa owners see multiple postings - or so it seems of some of the spas by either individuals or spas themselves and they start to do it as well. Sort of a Monkey See, Monkey Do. Like I said, English not being their language of communication, they do not understand why others can do it and they cannot.
Anyway, I am waiting to see what fallout, if any, there will be from your action. And I should mention that like I said earlier, I support your Action but for now, I encourage you to have a Appeal process and also initiate a TIMEOUT period of maybe a week or so before they are reinstated rather then an outright ban.