This happened to me. We brought our then 2 year old and 4 year old for a winter stay in an apartment in the mountains.
The owner said that he usually charged a small fee for the toddler/cot but would let it go. I said thank you and that was that.
The heating didn't work properly and we were so cold, we all slept with out clothes and coats on in the one bed. We were just staying 2 nights and we spent our days sightseeing so weren't in the house much. He kept telling us how to heat the house but it was the most rudimentary system and it just wasn't working. There wasn't enough water to have more than a perfunctory wash. I certainly couldn't have washed my hair. The whole place was freezing!
He contacted me later and asked me to give him whatever the max rating was. I said I was happy to give a good review as the house was gorgeous but couldn't give the full stars due to it being so cold.
He sent me a really horrible, snooty, snappy email about how he hadn't charged us for the cot and we got a pretty good deal. Basically saying the we should have accepted paying money to freeze in hus house because he put a cot up for us and didn't charge £25 a day for it. The thing is, we actually live in a beautiful, cosy, warm apartment near another scenic tourist spot and I'd wished I'd just stayed at home.
We didn't stay an an airbnb for a long time as we were so put off. I didn't leave a review at all. Things can sometimes get nasty so I decided to leave it. I'd once left a negative review on TripAdvisor about somewhere I'd previously stayed (in Italy).
Our toddler had an accident on their premises and had to go to hospital. I understood that these things gs happen, but the way the staff treated us was absolutely appalling. I've never seen such utter coldness and lack of compassion for a small child in my life, which is out of character for the Italians generally.
I was sobbing holding my injured child in reception. He was screaming in pain and i was desperately asking for a doctor, or an ambulance or the details of a nearby hospital and they looked at me with the most callous, unfeeling expression of contempt. We got a taxi to a hospital nearby and our child's wounds were treated.
When we got back nobody would acknowledge what happened. Nobody would speak to us, until a manager eventually had to talk to us and she just tried to make excuses and blame me. It was such a horrible experience that even my husband was crying at the end of it, and I have never seen him cry apart from a few times when someone has died. It was dreadful! I left a review, and they commented back that I was an awful mother and they felt sorry for my child having oarents like us. Another member of our party left an equally scathing review and the staff left her a baffling reply, basically saying that she was only saying this because because we had been so rowdy that they had to call the police. This never happened!
So I don't leave bad reviews if I can help it but only leave good ones if they deserve them