How does this happen?  I'm not sure I see the procedure.... anyone?

Good morning!  To sell credits, you first set a price either per credit, or per bundle of credits. Then you let everyone know which methods of payment you take. (For example, I take paypal or Amazon e-gift cards), and provide the buyer with your email so they can send the payment to you. Then, as soon as you receive payment, you come back to paperback swap and click on their name and then click 'give credits', and transfer however many credits they paid for to them.  I hope that helps! :)