Who defines the title of Internet marketing expert?
The site/business owner? If so most of their main pages should rank highly for Internet marketing related keywords
Former and current clients, this is possibly a better metric
Most information on what is needed to get a site ranked highly in Google is in the public domain, that said it is also mixed with plenty of incomprehensible gabble.
People who are really good at
SEO, have a website that ranks highly in competitive sectors, they have a systematic approach to their work, they experiment regularly, have an abundance of patience, do not make false promises and seldom have time to post on forums.