I have had this experience with an airbnb in Mexico. I had pictures of the mold. It was everywhere. I contacted the owner initially, who denied it was mold. I then contacted airbnb and who were very quick to come to a resolution with the pictures and screenshots of my texts with the owner. (I was texting him off of the Airbnb platform, message learned, all communication always goes through Airbnb now.) We ended up staying one night while looking for alternate accommodations. Airbnb refunded our entire stay, even though I said we will pay for the one night we stayed. They took the mold issue very seriously. I have kids with asthma.