I can always tell the difference between a non-native English speaking writer and somebody who's just stupid - the sort of grammatical mistakes stupid people ma

I can always tell the difference between a non-native English speaking writer and somebody who's just stupid - the sort of grammatical mistakes stupid people make are very, very different than the ones that people make when speaking a second language. Of course, sometimes the non-native English was so bad it wasn't worth wading through it, so that's still sort of a good signal.