Many clients I’ve worked with want help with grammar, proofreading and editing. They ask me to pay attention to details. They are tired of working with virtual assistants who let correspondence and emails go out with spelling and grammar errors.
Make sure you proofread anything you do for clients for correct spelling and grammar. If writing is not your expertise, don’t market yourself as a writer. If at all possible, ask someone else to proofread for you. Another set of eyes never hurts.