Well, that's how it should be, but unfortunately, that's not always the case. Pretty much all over Southeast Asia, many private schools with good reputation, international schools and language centers only require a bachelor's degree (NOT necessarily in teaching - can be completely unrelated, which is bloody ridiculous) and a native speaker status (or proof of fluency if you're a non-native), some ask for TEFL/TESOL/CELTA in addition to that. Sadly, actual teaching qualifications, experience and relevant educational background are seen as a plus (and a bargaining chip for better salary), but not as a non-negotiable requirement. There are obviously some exceptions, but the massive shortage of foreign teachers means that even proper schools are often forced to fill their positions with people who don't necessarily have appropriate qualifications.