How to deal with rude customers?

I am very detailed in my profile and I also respond to everyone within 30 minutes and even 5 minutes after they have sent me the message. There was this 1 rude person who contacted me and got angry at me because I said I was available. I just found out about a certain appointment right when i landed from a flight from vacation and didnt have a chance to update my calender right away. My flight got in around night time. My calender is very much up to date but this one person who had contacted me got angry that it wasnt up-to-date. I explained that I just found out about this appointment right when i got service once I was off the plane. But he continued to bash me and say i was a "bait and switch" i feel like that was a little bit over exaggeration being that I responded to him in about 20 minutes explaining myself (he wanted a stay that was about 1.5 months away) I responded right away in time for him to find someone else. When unexpected circumstances happen it is hard to update your calender when you dont know when youll need it off. My question is how do you deal with rude customers. It was out of my hands to know exactly when this appointment Would be since I had no say in what week it would be in August. He continued to sent sarcastic messages and saying I was "bait and switch" because my calender wasnt updated for that 1 week he needed. I feel like i was responsible enough because I cannot predict the future. I messages him politely and apologized. I am a very successful dog-sitter and have many clients come back and they are really happy with their sitting. I always make sure i tell people right away if their dog is a good fit or schedule a meet and greet.