I cancelled once because I was sick. Got charged.
I was late another time, got a text message ten minutes after session should've started to see if I was still coming in or not.
One time I turned up. He was more than 20 minutes late after asking me to come in half an hour early. I walked out. Ten minutes after that, I got a text saying he was ready to see me. I said he could get stuffed because I cancelled a coffee with a friend to fit him in earlier and he was late and I wasn't going to pay for half an hour instead of an hour if he had to leave early. I didn't get charged. Although I was upset for two weeks and didn't get a reply. And he didn't apologise until I told him I thought it was rude what he did.