Bought an item on Ebay, seller wants additional shipping payment?

they're not allowed to do this- it's their responsibility to work out the shipping costs before hand--- it's not worked out automatically. they've obv been to the post office and been told it's more. this has happened to me a lot and i just lose out cos i know it's not fair to ask for more money after. if it was, people would always ask for more money for shipping to get more money! unless ebay has calculated the price for the wrong country, ie thought u were in the uk then they have no right to say 'the amount of postage you have paid doesn't cover the actual cost' cos they're the ones who have calculated this! i'd ask for a refund or say you wouldnt have bought it if u knew it was gonna cost more- they may just let u have it