In an insert magazine from The Washington Post called “Capital Business”, for March 12, 2012, Eric Yaverbaum has an interesting article on p. 39, “Be wary of buying Facebook ‘friends’”. The only online link is the pdf for the magazine, here, and you have to thumb down to that page.
He talks about companies that will sell, say, 10000 Facebook “likes” to give you (or your small business brand) the appearance of a following. But these parties probably won’t stay with you, and in the long run will lower your “EdgeRank Score” (link). I tried the trial service this morning (yes, you have to subscribe to EdgeRankChecker to get the service permanently).
Here's Isaac Wardell's video on your "Facebook Engagement" measure, Edge Rank: