Your schedule can vary dramatically and is affected by student ratings (even unfair ones). You can find yourself with a massive drop in income for no reason at all. It isn't suitable for full time work for this reason. You can't rely on it as your sole income and those who do often seem stressed and anxious in the teacher community forum due to random drops in schedule classes.
After 5 years of working there, my contract was terminated unfairly. I had received a fair warning for having 4 Internet disconnections in one month, then I made sure that didn't happen again, but a couple of months later they said I had additional disconnections (which I didn't) and they terminated me for that reason. I did, however, use the cancellation feature due to studying for my teacher's license, but cancelling classes in advance is allowed and shouldn't be a problem.
There are also many hours of unpaid training you must go through continuously, year after year. I can understand unpaid training in the beginning, but it doesn't stop. They expect a good standard of teaching and continuous professional development, but the pay doesn't match that.