I have been teaching now in Thailand for six years and am pleased to hold a TCT license. I prefer to teach in government schools, because I know that I am only able to encourage the students to use the English they are taught. I have found that blame only comes to the farang teacher when he fails to involve the Thai teachers. Complaining about the students and other teachers actions really only makes tasks more difficult. When I fail a student or give low grades. I always suggest to the Thai English teacher that as they see the student more than me, that they must feel free to alter the result for the student the way they see fit....and 9 times out of 10 they change nothing, as my mark usually reflects the Thai teacher grade too. In fact I am then asked to speak with them and their parents too.
My stuggle is always the time I have to spend with each class and find my English only lessons are undermined by other imported teachers who will use more Thai in class then English when the previous year I taught them using English only. My simple advice is when a class goes missing! - make sure the workload that you would have taught isn't so big that a hand-out to the class can be digested easily for revision at another date.