I pay for Facebook (ads, as well as boosting posts). That makes me a customer, I guess.
How does one pay for Facebook? Is there a premium service I'm not aware of?
Same way Google do with adword on their search page.
I run ads on Facebook for several Facebook pages and additionally promote their posts (using the per-post boosting) fairly regularly.
In your example though the Ads are the product you're paying for. Not the Facebook account that is purchasing them, though I see how they're inherently linked.