err..
im not siding with the seller here...cos i also reckon asking for feedback in advance sounds pretty dodgy...but what postage option did you pay for?

ive bought an item from ebay UK about a month back which was sent via regular air mail and it took 27 days to arrive and there wasnt any major public holidays during that time either!!!

On the upside, if the seller does not have any proof of postage cos it was not registered, then theres no reason why paypal wont favour your claim.