Nobody is immune to spelling and grammatical errors, not even me. It doesn't matter how many times you proofread your content, sometimes an error slips through the cracks. But, too many errors in your writing are bad for article writing services business and can also hurt your reputation over time. If customers are annoyed by poor grammar on social media or on a small blog post, just think about how they will feel if they receive an email or eBook laced with these errors.
I've ranked websites in the past with spun content, and now they are still on #1 position of google. First year (2014) google found me because my spun was really bad, many paragraphs were just copied and my position drop from #2 to around #20 after a panda update. Later I cleaned all my text with better spun (I didn't buy any article!), my ranking went up again, and with more backlinks I reached #1 and it is still there