@Colleen253 What if you approached it from a standpoint of you’re offering to help THEM by NOT allowing them to use it. So...
”we just had a really unfortunate incident where a guest thought they knew how to use the fireplace but things went awry and it was a real bummer that they ended their stay by paying for smoke remediation. What do you think would be good for your stay? Are you a fireplace expert? Were you planning on using the fireplace? Would you need a fireplace tutorial? Or would you like me to leave some led flameless candles for you?”
A message like this sets the stage that there are consequences for ignorance and you’ll help them make better choices. This is what I would do if I were willing to let them use it.
alternatively, the message could say “unfortunately we had a guest cause a house fire, we’ve been able to remediate the smoke damage but our insurance company has insisted that the fireplace be disallowed from use. Of course we’d be happy to host you without the fireplace or I’d understand if you’d prefer to cancel. Please lmk either way by xxx “
and then it isn’t your fault but the bad guest and the ins co are the bad guys.
You know best if your house is worth less without that amenity. Good luck!