That's hilarious. They are lucky they aren't dealing with me as they would have recieved a large dose of sarcasm. If they can't check and change a fuse in under 5 mins they should go and find a new job.
However, it's worth pointing out that the cigar lighter socket wasn't originally intended for use with anything other than a cigar lighter! In fact when they invented the cigar lighter socket, there weren't any of these amazing electronic gadgets such as sat navs on the market. Unfortunately, when sat navs and the like started to appear, the only 12V outlet on the dashboard that everybody had was a cigar lighter socket. The socket is actually not very suitable for use with delicate electronic gear as it is generally grubby and doesn't provide a solid, reliable connection. But since its all most cars have, we are stuck with it for the time being.
But that is no excuse for dealer incompetence. My guess is they will try and charge you for changing the fuse.