Why should I hire a professional digital marketing agency to promote my business online?

This video, https://www.youtube.com/watch?v=9uJqhjXyZM4, can also be seen at https://www.youtube.com/channel/UCFE6qpvSvg5BIx2nYJz3jvg.
See the rest of the story at http://tvblog.insupolycarbonate.com/why-should-i-hire-a-professional-digital-marketing-agency-to-promote-my-business-online/