I am having a difficult time understanding Facebook's internal "e-commerce microcosm" and what it allows Facebook App developers to do (and what it restricts them from doing).

Two use cases:

• I'm an e-com retailer selling clothes and coffee mugs (real-world goods) on my website; I want to write a Facebook App that allows Facebook users to buy my real-world goods from inside of Facebook using real money ($ USD)
• I'm highschool student trying to raise money for my senior class trip and want to build a Facebook App that allows Facebook users to donate to our class using real money ($ USD)

Are these two scenarios possible? If not, why (what Facebook policies prohibit me from doing so)? If so, what APIs do I use: Payments or Credits? And how (specifically) would it work? Do Facebook Users have to first buy "credits" (which are mapped to $ USD values under the hood) and pay/donate with credits, or can they whip out their credit card and pay/donate right through my Facebook App?

I think that last question really summarizes my confusion: can Facebook users enter their credit card info directly into Facebook Apps, or do you have to go through Payments/Credits APIs as a "middleman"?