Found this article from GroupHigh's Outreach Marketer about vetting influence. As the opportunity grows for more merchants and content sites continues to grow, choosing the right partners is so important.

How are Marketers Vetting Influence?

How do you vet your partners?

Personally, I don't just look at the number of followers or likes a site may have - I'll look at comments, engagement, etc. as a way to evaluate their influence.