my reputation as a buyer is established so i'm not fussed if a seller doesn't  leave feedback.

i don't care if a buyer leaves me feedback or not for the same reason.

i no longer leave feedback as a buyer but will usually contact the seller to tell them the item arrived safely.

however i ALWAYS leave feedback as a seller as soon as my buyers make payment to demonstrate my genuine appreciation of their custom.  i think it's important for the building of a professional relationship.  i have many repeat buyers.  a thank you is part of good service and one component of a whole positive buying experience.  imagine going into a bricks and mortar shop and the assistant not having the time of day to thank you, smile or say hi.  they wouldn't see me again.  sellers need buyers more than the other way around.