Probably they have calculated a "facebook credit score" based on your facebook posts and your relations on facebook, and based on the websites you like and visit and have decided you have to be billed daily.
I'm not sure why people would want to advertise on a site that likely has the worst click-thru rate on the entire web. I can see it being okay if it's something that's specialized and needs to be perfectly targeted, like running for college president, but I would imagine money would be better spent elsewhere for almost any product you're selling.
It works well for us. We have a B&B. We target a certain segment of the national population in our South American country. We bid low & get clicks for about 2¢ each. About 40 to 50% become fans.
It definitely brings us reservations that more than cover the cost. We now have just under 16,000 fans & every Saturday we post a news item with rates or special offers along with our email & website link that gets lots of activity, questions & site views.
We run the ad campaign before national vacation periods & put it on hold during the slow months.
If I understand correctly, Facebook is the worst advertising opportunity on the planet. Nonetheless, Fortune 500 companies who are crazy to use that have pushed its valuation to the highest that has ever been for an internet IPO.
Having said all that, Facebook bills once your account reaches $30. It is not even possible to prepay if you request it.
This billing practice is even more annoying than Facebook's failure to create an ad system that is profitable for everybody.