Well he should pay-up - he is legally obliged to.

But to be more precise, what I am saying is that I should have made the appropriate enquiries BEFORE the auction ended and satisfied myself that the laptop existed and was as described, and that the seller was trustworthy etc etc. If you can bothered to read the tutorial on Ebay you will see that what I am saying is exactly how Ebay expect it to work. Once the auction has been won though, the time for asking questions is over. Pay-up.

The guy selling the laptop that Karl has won could be totally legit. If Karl refuses to buy because he has now decided that he was not happy with the terms of the auction (which will have been something like this is the laptop, is in good condition, if you win it it will be posted to you), the guy could theoretically sue Karl for breach of contract. In that instant the Court will not be interested in Karl wanting to make sure he is not getting ripped off. They will look at the terms of the auction, express and implied, and that Karl accepted those terms by placing a bid.