I have taught at 5-6 schools and experienced positive and negative times. Unpaid, complained about without the chance to challenge or know the source, unusual requests for urgent work that is shelved or cancelled upon completion. The biggest problem with Thai government schools is the teachers having to produce their own lesson material and curriculum. There may be 4-5 English teachers at each school and each teacher will have his own curriculum with no set teaching or exam standard among the entire school.
The positives, having white skin enables you to walk into a school and teach without formal qualification or a visa or work permit. The barriers to entry are extremely low and biased towards people of western countries. Good experience, but not a sustainable career path unless recruited into an organized school or teaching system.