Facebook, YouTube, Twitter, and other social media sites are constantly changing. You want to hire someone who has an ongoing commitment to keeping current. Put their knowledge to the test. Have them explain the changes. The response should help define your selection criteria. It’s also a good chance to see how well the person can explain things to those who may not be experts.
Your potential marketing partner should also have different strategies for different social media platforms. What works on Twitter, may not work as effectively on Facebook.