This is actually a great idea for Facebook - don't sell Likes in absolute numbers, sell them normalized to the fraction of total Likes for the users Liking you.

So I could buy 10 "Fractional Likes" and get 20 users who each only have 2 total Likes (including this one) = 20 * 1/2 = 10

OR I get 10,000 users who each have 1,000 Likes each = 10K * 1/1000 = 10

...which seems a reasonable ballpark for resolving it in an automatable, economic way.

"Don't allow Likes over X" kind of sucks since what happens to legitimate Likers? I'm not a clickfarmer, but I've Liked way more than 5 things.

My News Feed has turned to crap (probably because of it), but that's a whole 'nother story.