The most successful e-marketers sell products about…how to become a successful e-marketer. There's a trend here.
Writers who write books and articles about…how to be a published writer.
Entrepreneurs whose entrepreneurship is about…entrepreneurship.
The networking guru who uses his network to…sell books about how to network.
The personal branding expert whose personal brand is about…personal branding.
These are what I call "meta-careers." Generally, it's best to not seek advice on the topic from people involved in a meta career.
The best advice on networking will come from someone who is not a professional networker. The best advice on entrepreneurship will come someone whose entrepreneurship is not selling books and workshops about entrepreneurship. Writers who write about anything other than writing for a living usually have the best advice on writing.