I've been hosting for I think 2-3 years now. I've learned those guests will come every once in a while. They come with all kinds of baggage, attitudes, personalities, pet peeves, etc. It can be disrespectful and hurtful to get such persnickety feedback, especially when you've gone above and beyond to prepare, ensure their comfort and safety, and provide tourism tips. I just had a tough review a couple weeks ago myself. Take it all in stride and keep moving forward. On the bright side, each tough review makes you better. Over time, you end up with lots of positive reviews and those unavoidable negative outliers mixed in.
I'd say don't worry about the refund for that small stuff. I've only refunded someone in extreme circumstances that impacted their travel or sleeping experience (hurricane, flooding, funeral, etc.).