Your website should act as your best marketing tool, so why not hire a marketing firm to build and maintain your site? Marketing is a working project, constantly developing, changing, and progressing. Websites are the same way, which is why marketing firms understand the big picture. They envision website development as a process rather than a project.
By following best practices, your website can act as your main marketing mechanism. Start by defining the purpose of your website in terms of marketing goals. Are you looking to gain market share? Support customers? Increase sales? Drive traffic? Your development company will be able to build you a website that works toward achieving your well-defined goals.