@Elle82 Since these guests are bound to leave a bad review no matter what (unless they tried to extort you for a good review, as mentioned above, in which case Airbnb should remove their ability to review) , I'd send them a charge for turning off the irrigation system and killing all the plants. Those plants will probably be somewhat costly to replace. Of course, they will refuse to pay, but maybe they'll back off the refund game if you do this. They're manufacturing faults, when in fact, they caused damage.