There is a specific point in the human psyche where greed and gullibility intersect. Somebody found it and set up a sign there that says "We have [thing you want] that we can't sell because [contrived reason] and so we're giving them away to people who Like this post on Facebook!"
There is no free stuff. There never was. How did all of these people make it through childhood without finding their way into a van with "FREE CANDY" painted on the side? This is the exact same trick.
Remember, when you click "Like" on something because you were baited into it through greed or crass emotional manipulation, you are depriving an Indian of a job.