@Martha68 Your beautiful space is located in one of my favorite spots in California! Unless you can identify some shortcoming of your hot water heater that you would need to compensate the guest for, I wouldn't do anything. If the issue is raised in the review, a professional response (not defensive) would acknowledge the issue and what steps you took to address it such as you had a plumber confirm the heater was operating properly.
It is reported in many discussion threads that some guests will try to get a discount or refund by making complaints and implying a negative review. Air BNB does not support review "blackmail" by guests. Of course all feedback should be investigated, but refunds or discounts should only be applied for legitimate guest inconvenience. Good luck with your new business. You are already off to a great start!
