JoeLister actually does not transfer any money from eBay to Amazon.
When a buyer purchases an item from eBay, we ask Amazon to fulfill it. Then, Amazon bills a "multichannel fulfillment fee" to your Amazon account: http://www.amazon.com/gp/help/customer/display.html/?nodeId=201119430
So, you're not paying the full price of the item to Amazon but a charge to prepare and ship the package to your eBay buyer. The money that your buyer pays you on eBay/PayPal stays on eBay/PayPal, and eBay/PayPal pulls their own fees from there or will bill you separately.