Looking to get more popular on Facebook? Alex Melen will sell you 1,000 "likes" for about $75.

Melen runs an Internet marketing company. About six months ago, companies he worked with started coming to him more and more with a simple problem: They had created pages on Facebook, but nobody had clicked the "like" button.

"You would go there, and there would be two likes," Melen says. "And one of them would be the owner. And people right away lost interest in the brand."

For the right price, Melen can fix that.

Facebook knows an incredible amount about hundreds of millions of people — what they like, what they want, who their friends are, where they live. This is the key reason why investors think the company is so valuable. But that value only holds up if the data is real — if all those people actually like what they say they like.

When Melen sells likes to a company, he goes through an intermediary, who in turn could be working with people anywhere in the world. The people on the other end are just doing it for money. They get paid a very small amount — 10 cents, say — each time they like a company.