Dear Potential Employer,
I presently verify and proofread documents for official meetings of the United Nations, which uses UK English, and am well able to help you with your article. It is indeed a good idea to have articles reviewed by a "third eye" before you approach your publishers. I am familiar with the needs of marketing, having worked in marketing in the pharmaceutical industry,rising to marketing manager.
In undertaking this assignment, I would review your article to fix any typos and grammatical errors, edit and revise it if necessary for logic and to clarify the flow of ideas, and send you the draft highlighting all changes made (the redline). Once the article and changes have been agreed, I would supply you with a clean copy.
During the course of editing your article, I would review similar material if I felt it necessary.
Please do contact me to discuss this in greater detail.