Ask HN: Ways to transfer money among users?

I'm building a web app that will (hopefully) include a feature that allows users to send money to each other. I'd like User A to be able to enter his credit card info and charge money that User B would receive in the form of a check or direct deposit.

My initial research indicates that I can't just get a merchant account, accept payments, and then write the checks myself. Based on Tipjoy's experience, I'd need money transfer agent licenses for this. Is that correct?

Assuming it is, anyone know any good alternatives? Amazon FPS is the obvious choice, but it has two major downsides: (1) it's relatively expensive and (2) users have to login to their Amazon account to make the payment, which adds another step to the process and looks unprofessional.

Anyone know any alternatives to Amazon FPS for this situation? There are sites like Eimburse (http://www.eimburse.com/) that seem to pull this off without all the licenses, but I have no idea how they do it.