There are a ton of foreign teachers in Thailand. Most of the people that I know are either retired or are teachers here in Chiang Mai and of all the teachers I would say that only a handful of them have jobs that I would consider worth keeping.
For many years Thailand has been seen as a place where someone who is not actually qualified to be a teacher can come and be one anyway and in a lot of ways I feel as though this is a very bad trap for young people and they need to figure out that this is NOT a good long-term plan and simply work a few years and then get out.
A lot of people get used to the way of life over here and prefer it over life in their home countries and stay a lot longer than I think they should and end up screwing up their financial futures because of it.
When these jobs are presented online they are most often shown in a very different light than what is actually the case. Photos will be shown of well-behaved kids in non-crowded classrooms being very attentive and respectful to the teachers as they dutifully go through the education process in a calm and controlled manner. The truth is the polar opposite of this.
What is the more likely or basically guaranteed situation is overcrowded classrooms with disinterested students that don't have any idea what you are saying to them and just like kids around the world, they will use any opportunity to horse around and turn the classroom into chaos at any given moment. The only way to keep them quiet is to give them a bunch of busywork to do and while this works, it does seem a bit mean. Also, the kids just copy one another's papers so they don't actually end up learning anything.
To make matters worse, these jobs that are being offered to just anyone with a degree who is reasonably young is that the salary is normally very bad in Thailand. A starting teacher can expect to make around 25,000 to 35,000 Baht per month, which is in most cases less than US $1000 a month.
Thailand is an inexpensive country, but if you live your life at all and have any hobbies or spend money on leisure time, you can be all-but-assured that you are not going to have any money at the end of each month. Most of the teachers that I know don't manage to save any money at all and even though I am quite frugal and live in an inexpensive rental house, I struggle to put away just a hundred dollars a month.
This is no way to live and teachers need to realize really early on that this should not be considered a career but rather an experiment or a chance to explore for a year or two before returning to their own country and getting a real career.
If while you are in Thailand you end up loving the lifestyle here, put a photo on your fridge in your home country to inspire you to not buy into consumerism and to save as much money as possible for retirement and then do so early.
Most of the retirees that I know here don't have enough money to retire in their home countries, but can do so here quite easily because it is much cheaper than in the west.
Now onto the "good" teaching jobs. These jobs are few, far between, and have a ton of competition to acquire them. In order to get one of these jobs you need to be exceptionally qualified and will likely need to have certifications that would enable you to be a teacher back in the west as well. I know one person with a job like this and he has a PGSE, a degree in Physics, and is a certified engineer. He works at an international school and makes really good money. His job is one of about a dozen that exists in the entire city of nearly a million residents.
The rest of the teachers just have jobs like me where they get paid just enough to not quit and they are very replaceable should they ever feel as though the job is not for them anymore. As a regular peon teacher like me, you have zero leverage as far as contract negotiations are concerned because you are not actually qualified for the job in the first place. My Engineer friend could be making a lot more money by simply going and doing engineering work and therefore, he is able to force his school to compensate him very well.
The moral of the story here is that teaching in Thailand is probably not a good idea unless you are qualified to be a teacher in your home country. I wouldn't recommend it but if you do decide to do it, I implore you to see it as temporary. I've seen way too many people screw up their futures by sticking with these rather terrible jobs for too long.