SEO Content Writer

I am looking for an SEO content writer to join my team of SEO professionals. You must be able to produce 100% perfectly written english material for my niche. Anything with errors or that is not 100% perfect english will not be accepted. I would prefer someone who is native English speaking for this task and preferably someone with a background in content writing. We currently have over 40 websites so there is plenty of work for the right person. Please bid per article / document thats a reasonable in size. A sample document will be asked to be produced before picking the final person for this task.