Anyone who has ever worked in a school of any kind in Thailand can tell you that you're bound to run into a fair share of issues: getting work permits and visas, pay discrepancies, untruthful job descriptions, and the lot. That said, and correct me if I'm wrong, it seems that Thai government schools are the worst of the lot.
When I started at my current government school going on two years ago, I didn't know any better and was hired through a [terrible] agency that fired/hired people on a basically a weekly basis. Teachers weren't paid the correct amount (as in, ever), and even if they were paid at all, it certainly was never on time. Every teacher (myself included) at my school save maybe one was fired for one reason or another far before the semester ended, but because we liked (and like) the school, we were loyal and stayed on anyway; it wasn't fair to our students that their teachers were contracted out to a highly unprofessional agency.
Long story short, through strength in numbers and proving ourselves valuable teachers to the school, we got the school to hire us on directly the next term and have been ever since. In a perfect world, that would result in no further "major" problems, and for the most part, I'd say it's been relatively smooth sailing... well, as smooth as working at a Thai government school can be. That said, especially as a warning for you newbie teachers out there, problems still do arise.
Just this week, for example, the finance department at our school (one of many departments) decided that, since we didn't sign our names on a clipboard for the first six days of May, we were going to have said days' salary docked from our pay this month, even though our signed contracts say nothing of this and we were told to start coming to school during the second week of this month. Supposedly, the Thai teacher in charge of the foreign teachers has resolved this situation for the returning teachers, but because the new teachers haven't signed their contracts yet, they are going to make roughly half this month of what was verbally promised. ...And some other minor crisis is bound to pop up soon as it always does.
I can certainly understand Thai schools' mentalities towards foreign teachers; just because we are English speakers, we make often three times what teachers working there for years make. We often have lighter workloads (at least in terms of periods taught per week), and there are many duties that we are often excluded from.
That said, and I'm generalizing here based on my experiences and those of many other teachers I know here, schools feel that they are doing foreign teachers a favor. The reality, at least for most of the teachers at my particular school, is that we stay because we genuinely like the students, the people we work with, and the school in genera l- not due to the salary. If you're a teacher because you actually enjoy teaching and are in it for the long-haul, a 30-40,000 baht monthly salary is nothing, especially considering how relatively easy it is to find another similar job. I make twice as much working for a language school part time each month than my full-time school, but actually enjoy teaching at my government school. Call me crazy, but I certainly can account for the high turnover rate.
My point is this: if you allow a school (or any employer, for that matter) to treat you in a certain way, it will continue to do so. Especially if you're a new teacher, get everything promised IN WRITING so you at least have some legitimacy. Some things are unavoidable, and you obviously need to pick your battles.
One teacher I work with has been at our school close to ten years, and the school still causes the same issues with him, among many being the nickel-and-diming and seemingly weekly minor crises we all face. To me, the salary is honestly not that big of a deal; it's the [lack of] professionalism that drives most teachers out of government/public schools here in Thailand after only a very short time.
Am I saying all schools are like this? Absolutely not. I'm sure I speak for a lot of us [teachers] when I say that I genuinely like working with most of my students and colleagues, both Thai and foreign. I'm reminded of a tweet by Ajarn.com a few months back that said something along the lines of, the longer a teacher is at a school, the less likely he/she is to put up with the bologna the school dishes out. Teachers get worn-down by the constant barrage of issues that shouldn't even be issues in the first place.
As unfortunate as it is, especially for the students facing constant teacher turnover, I couldn't agree more.