you don't HAVE to leave feedback. It is voluntary.
As an ebay seller, I don't understand buyers who would rather slam my FB than get a refund or replacement. I am always happy to work with a buyer to get them what they want. But once they leave me bad FB (and some do BEFORE contacting me), that's it, all bets are off. You don't get to leave bad FB AND get a refund, in my book.