@Barbara2155 People who start out complaining about things, unless it's actually an issue you need to address, like the fridge or the hot water tank isn't working, you can't give a good experience to, and throwing a discount at them doesn't change that. They are determined not to have a good time and will find myriad things to complain about.
Nor can you ward off a bad review by bending over backwards for these types. They almost always leave bad reviews.
So save your going out of your way for guests for the nice, appreciative guests, not the complainers. With those, just be polite but firm. "That is clearly mentioned in our listing information. It's unfortunate that it doesn't seem like you read the available info before you booked."