If you set up a dispute through Ebay or Paypal and post the item back by a trackable signed for postage service and it is received by the seller they will have to refund you automatically.
Ebay/Paypal will expect you to add tracking info to the dispute so they will know when the item has been returned. I would also make sure you take pictures of the item and also the packaging you use in case the seller tries a fast one(saying you have damaged it or something). It would also be useful to have a copy of a newspaper with the day's date in the picture too.
Leave feedback after the refund has gone through not before.