DH bought something off ebay that was pick-up only. When we went to collect it (a 3-hour round trip), the seller had forgotten to give us one essential component, which DH didn't realise until we got it home. He contacted the seller, who has agreed to post it to us but wants DH to pay. He has agreed as it's only £1.75 and he got the item for a really good price to start with, but at the same time he's a bit grumpy over the principle- why should he pay for the seller's mistake? WWYD?