@Thomas669 at this point you will be reviewed either way, so best to do everything based on what you feel is right without feeling hostage to the reveiw, bc that is out of your control.
Bed comfort is subjective
Bugs happen
So... My tack would be "thank you for letting me know. Is there something that you'd like me to do for you?"
And then see what they say. None of us can eradicate bugs from the planet & certainly not in the tropics.
I wouldn't necessarily offer to refund anything but I would almost always offer to let a complaining guest leave. Why? bc either they are complaining bc they like to hear the sound of their voice and they won't leave but you will have offered (covered your bases with CS). Or they are complaining as a way to fish for a discount. No, no discount, but if you're unhappy you may go. (covered your bases with CS) Or they feel strongly enough about their complaints that they want to go. Well, then I'm glad they're gone bc otherwise they'd keep complaining, quite possibly cause problems for your unit & maybe even complain enough after the fact to get CS to refund them. And the only thing worse, in my book, than not getting paid and not hosting someone is not getting paid even though you DID host them.
But, I'm a host that would rather have an empty unit than have a bad guest. Every host situation is different.