Hi,
Please read what I have to say, all I want from you is to be rational. Nationality does not define a writer, it's his knowledge about the respective language's grammar and understanding of vocabulary usage that sets the parameters. I beg you to be logical; rely on freelancer's testing system, all of the writers here have to pass the "English Language Test", simply tally bidders' scores and filter the best out of them. If it does not satisfy you, a better offer I can make is of a free sample, only to prove that natives are not better than me and it simply does not make any sense. Get a sample from the native writer you choose and one from me, compare both and you will get your answer. It takes patience but it will help you find the best writer who could actually turn in the quality you are searching for.
Sincerely,
Cheryl.