eBay

A buyer paid an item by mistake and sent me a return request. I want to know if I accept a full refund for him does eBay will credit me Ad fee standard?  

A buyer paid me for an item (3200$) and immediately sent me a message asking to cancel the sale because he bought the item by mistake. When I proceeded refund I found that my available fund at eBay become -432$Why I have to pay fees for a sale cancel...