>You may be right there. On the other hand, this woman says she now applies a simple rule rather than a complex test and she claims it works fine for here.
I think this is a standard criterion in the better-quality language schools - having a native speaker.
It should, indeed, work in many cases - given that most non-native speakers will have some accent. On the other hand, some test may still be appropriate, to ensure that the candidate for teacher knows grammar, etc. And perhaps a short conversation in the target language.
Difference in opinions hath cost many millions of lives: for instance, whether flesh be bread, or bread be flesh; whether whistling be a vice or a virtue; whether it be better to kiss a post, or throw it into the fire... (from Gulliver's Travels)