Italki and teaching online (because I have some students outside of Italki but most students are from here) has been my only source of income for 4 years now and I wouldn't change it for a traditional job. Can't imagine working for a school, university or any other company where I'd have a fixed schedule, deal with evil colleagues and bosses and having to do what probably I don't enjoy doing. It has worked for me and I know many teachers here whose income is only from Italki. So it is really possible (if you take it seriously). 

Some people mentioned about being unreliable and variable but not different from someone who has their own shop, business or whatever. If you work as the owner of a shop or if you are seller and mostly earn by sales commission, then it's the same thing. Not to mention that working online from home you save even more money because you won't have expenses such as transportation and food that you consume outside.

I have only ever SAID NO (!) to 3 students! One wanted to sit the proficiency exam, but was only upper-intermediate! One had 2 children who could not sit still! And one had such a bad internet connection that I could see it would not work!

I control the number of students by asking a higher fee. At about $35 an hour there is a supply of students. At $40 an hour the supply dwindles to a trickle. If I drop to $30 an hour I get too many.

So PRICING is like turning the tap on and off.

The other way to control numbers is to open or close down slots on the schedule. If I need students I open up more times to catch more time-zones. Then I shut them down again.

Four years ago I was working what I consider to be reasonably full-time. I managed it by doing the pricing and time-zone juggling! I only worked for italki. Luckily I am now 'retired' and have a pension, so I do not need to work. I work as a hobby, and only for italki. If I have any advice for newcomers, it's - juggle! And yes, you may have to juggle in another website if you need to work full-time. I actually wonder if people realize just how much work is involved in working online. And how low the pay is when you factor in commission, exchange rates, tax, and all the unpaid hours waiting for students who do not turn up, marking homework etc. I would not like to have to support a family by online tuition alone. It's too variable... dare I say unreliable?

  Sophia : Thank you for your comment ! 

Thank you all  for your comments  !  

I imagine that there are a few very popular teachers who manage to pull it off, but I think it would be impossible for most teachers (including most top-notch teachers) here. Also, the few who do teach here full time and make an okay income of it probably spent years building up their reputation on Italki. I would imagine that Italki is mostly an income supplement for most people. So, either they have another job, or they work part time while their spouses (or parents, in the case of college students) provide most of their income. 

ETA: @Jay 

Keep in mind that teachers who turn away students are not necessarily teaching full time here, either. They may only want to work (say) 8-10 per week on Italki. If they have enough regulars for that, they may not accept any new students, or they may be quite choosy about whom they accept.