I am not getting upset. Maybe that's because my teachers rarely cancel, or they notify me early enough. Life happens and lessons get cancelled. It goes both ways. 

Unless my teacher tells me they are down with fever and then I see travel photos on their wechat...

Life has a way of intefering with our plans.

Actually, based on my teaching experience on italki, I would say that 5 out of hundred sessions may be cancelled by various students (usually cancelled for very understandable reasons).

I always re-schedule the session, and I do not get upset by any cancellation.

I have had it happen twice that I can remember with new teachers. Both times I requested my money back and took my business elsewhere. I understand that things can happen, but I also feel that customer service is important and that losing trust in the professor is a perfectly legitimate response to this sort of thing.

I have had good luck with some of the Spanish teachers here. If you want some recommendations, PM me.

I am in a similar situation as I do not have fast internet at home and have to drive to town to use skype. Also I plan in advance, so that I can combine the trip to town with other things to do. 

Within 42 planned classes I had 3 cancellations (from two teachers) within 24h before class.

One teacher cancelled in the morning (for an afternoon class) due to illness. The other one cancelled within 5 mins before class blaming headache. I gave both teachers a second chance but learnt the following:

The teacher who cancelled in advance, never cancelled again.

The one who "suddenly" had a headache cancelled again 5 days later - this time 24 hours in advance (but to late to book another teacher) - and said that he had to work longer next day. My guess is, that he packs his schedule to tight and I would never book him again. 

Within this 42 classes I had to cancel 2 times within 24h: Once in the morning (for an afternoon class) due to illness and once I was not even able to cancel last minute because I could not access internet that day. The second class I would have paid but the teacher kindly re-scheduled the session.

It is hard to give advice, as every case is different and you did not give more information. 

I'd had a lot of online classes and cancellations are rare. I generally give the teacher a second chance, but if they give a poor excuse, no excuse, or don't seem to care, I find another teacher. There are a lot of teachers available so you don't have to stay with an unreliable one. 

I did have a particularly bad experience with one teacher on another language site. She was completely unreliable but I was able to get my money back.