When English isn't a person's first language, meaning that, generally their grammar is pretty weak and spelling is never perfect, I don't think they should be able to review an article with something along the lines of "Perfect quality, beautiful grammar and no spelling errors".
I've seen this in this thread and many BST reviews where a person has talked about a "perfect" article but really when you have five poor uses of grammar in your review, you're not the best person to judge on "quality".
Basically, if you want to find a good value writer then ask for a recommendation from someone that has English as their first language.