Understanding eBay/PayPal fees

Selling things on eBay used to be a pretty simple and straightforward affair. The costs were fairly easy to understand and people, generally speaking, were happy. Then eBay bought PayPal which should have made things even easier for all concerned, but strangely (or not so strangely) has resulted in a multitude of costs, fees and other considerations that directly impact your bottom line. I wouldn't exactly call these "hidden" costs, but nor would I describe them as "well advertised" and could certainly catch the unwary seller off-guard. Here is a brief guide on what to watch out for.