The incentive to make fake accounts on Facebook is orders of magnitude greater than almost any other social network.
> One effective strategy we've employed not mentioned here is category mapping: if an account of type A, only targets accounts of type B for likes (especially if they ignore categories C, D, etc.), this is usually a high indicator of fraud. For example, one very common strategy is to create a fake account for an attractive female to friend many male accounts (especially relatively new accounts unaware of these tactic). This can be easily detected by analyzing the gender and account age of all targets and coming up with a diversity score. Low diversity score = likely fraudster.
Facebook has methods that radically exceed this method in both complexity, precision, and recall.