I recently read a forum post asserting that every professional should be able to write his/her own resume. The writer went on to say that, because no one knows your experience better than you, you are the only one qualified to do the job. I don't know why the "you have to do it yourself" attitude persists when it comes to writing your resume. It's essentially like saying you should do your own taxes because nobody knows your finances better than you.
For people who are comfortable writing their own resume – and can produce an outstanding one – fantastic. For those whose strengths lie elsewhere, there is no reason not to hire a professional. In fact, I would say that recognizing where you can benefit from others' expertise is a far more valuable skill than being able to write your own resume.
Your resume is an incredibly valuable marketing piece and often your only chance to make a strong first impression. Don’t waste those opportunities by using an unpolished or underwhelming document.