These questions always come up teaching English in different countries all over the world. Lots of times students or parents demand native speakers to teach them English and of course the perfect accent because as Urszula Calrk states:
A common and long-held belief among many in the English teaching profession is that the best people to teach spoken English are ‘native’ speakers of the language, especially the teaching of pronunciation.
This is often the only requirement for twice a week conversation classes where a white or let's say fair skinned bloke entertains the group with stories and jokes. Proper jobs that require a degree often discriminate application based not only nationality but sadly skin colour, too. Even if the job description doesn't state it, many teaching institutes lean towards candidates where they don't need to explain anything like: She has raised in England but their parents didn't.
Either it is laziness or simply satisfying costumers needs it's disappointing.
Successful communication is more a question of understanding, and being able to engage successfully, in the contexts of use rather than whether one is a ‘native’ or ‘non-native’ speaker.
Researches show that not only teaching English as a second language is more effective if the teacher speaks the native tongue of the students and knows the cultural background they are from.
But the importance of so many times praised accents or correct way of speaking are in fact diminishing. Replaced by a wider variety of English spoken by the international community in various trades. Where the weight lies on the understanding and being understood rather than the ability to replicate the perfect accent.