Until about a year ago when a client wanted to do that type of campaign they'd have me write ads for both Google AdWords and Facebook ads.
Now, nobody wants to hire me to do Facebook ads. But they do want me to write ads for Google. And, after a lot of split testing I can tell you why - the Facebook advertising algorithm is fucked and cannot possibly be fixed while the Google algorithm is top notch.
This doesn't mean the programmers at Google are better. What it means that is human nature makes it impossible for Facebook to give you the correct targeted ads.
It turns out that the search terms you use on Google are a very good indicator of what you might buy. If someone goolges "Blu Ray Players" the odds are very high that they want to buy a Blu Ray player. And if you send them an ad for a site that sells discount Blu Ray players there is a very high chance of them clicking on the ad and buying from that online retailer.
What you search = what you might pay money for.
But, that's not how Facebook works. What people post about on Facebook often has nothing to do with what they would really buy. Often they make posts making fun of products. Other times they post links to things they think are stupid and funny. They take the piss out of stuff with their friends in their posts.
What ends up happening is I type in "I'll never get married again" and a day or two later I get ads for engagement rings. That's not going to work. Or I post "can you believe how awful Attack Of The Clones is on Blu-Ray" and the next day I get an ad trying to sell me the Blu-Ray version of The Phantom Menace. Today I made a joke about the idiot who shot himself to protest gay marriage and I'm getting ads on how to make my own bullets.
Companies have figured this out. Because they can see how many sales they make via Google vs. how many they make through Facebook. So, now that the rush of "social media is the future" is over, companies don't want to throw money at Facebook for posting their ads on the pages of people who hate their products.
This means that in the long term Facebook is completely and totally doomed. But Google will thrive.