So your concern is the blackmailing and the eventual bad review that they have threatened you with. If these comments by the guest were on the platform all you need to do is write Airbnb on the platform, direct Airbnb to these comments and ask Airbnb that when the guest review is ultimately posted you will ask that it be removed based on Airbnb’s policy against retaliatory reviews.
If the threats were not on the platform you can still provide the documentation to Airbnb, though if Airbnb can’t easily authenticate them it’s possible that Airbnb will be forced to disregard them.
If so, come back to us as other comments on the platform (copy and paste them here then) might provide a basis for removing the eventual review.
We have many experienced and knowledgeable Hosts here who will candidly tell you whether you have a case or not for removing a guest review. Just give them the facts by copying and pasting the actual back/forth with the guest if Airbnb says it cannot remove the review based on what you say.
You do need to think about this key issue, whether there is anything you can do to prevent its recurrence.
Don’t feel a need to respond to the questions and comments below if you feel that your question has been answered and don’t want a further back/forth.
I suggest that the procedure for returning the key be a house rule stated in your listing. Further, your house rule, stated in the listing, should say something like “If the key is not returned per the house rule the property will need to be re-keyed and the expense charged to the guest (cost is easily in the ballpark of $X or more).”
I think your key should also state on it ‘do not duplicate’ although I think that is not a sufficient security procedure these days where at least where I live I can go to a kiosk and duplicate a key myself. You might want to explore keys that cannot be duplicated or some way to avoid needing to re-key the property when the guest violates your return key policy.
Does this mean you don’t have a copy of the key?
If every guest can copy the key during the course of the rental, isn’t that a security issue? Or maybe not because you say:
So, is the reason you re-keyed the property not a security issue (since a ‘chip’ is also needed) but because you didn’t have a spare key?
If the need to re-key is not due to negligence on your part you might also want to try to cover the expenses of re-keying with the guest, and then Airbnb. What do you have to lose?\
What if they lose that chip? If there is a cost associated with that, that should be stated in your House Rules on the listing. I am assuming that the chip is not easily duplicated but I wonder what the consequences are of the chip not being returned/lost.
Please consider mattress protectors and pillow protectors and other ‘guest proofing’ measures you can take to prevent damages or mitigate them. These protectors also make your property more healthful for your guests.