I used to leave feedback once paid but recently have been attacked with negative feedback form several eBay goons so I had to rethink my policy.
My current policy is one that a lot of sellers now have. I will leave feedback once a buyer does so and let's everyone know they have had a positive experience with me and everything with the product is okay by leaving me a postive feedback. The buyer is the one who has the last word on whether or not everything was done properly and if everything did not go properly then they simply contact the seller. This also will hopefully persuade hotheaded buyers from immediately leaving negatives and not contacting the seller to find out the who, what, why, and how the transaction went wrong and allow a seller a chance to fix a problem if and when one would ever occur. I always return postive feedback left for me but I need to be allowed to protect my feedback from people who just don't give a darn like joy bidders and ghost bidders who think they are having fun by destroying someone's reputation.