I can count on one hand the number of English teachers I've met in the ten years since I first came to Korea who were actually certified teachers back in their home country. If the proportion topped 2%, I'd be...
It's pretty often the case that Teaching English in Korea involves very little teaching and not a whole lot of English. This is perhaps the most important thing about all this that nobody ever tells the newbies. In other words, for a very large proportion of people coming to Korea thinking they'll be teaching the English language, the reality is that they probably won't, really.