A good judge is not swayed by reviews, although it's very hard to avoid reading them - people are already saying that the Harry Potter book is by far the favourite for this year, and it's going to be hard for the judges to resist that, if they want to. It's important not to bow down to the opinions of those on the panel that you think know more about literature than you do - hold on to what you really like and argue for it. You need to be able to come up with more than "I really enjoyed it" to justify a choice. You need to be looking at things like characterisation, whether you found the book emotionally moving, the new and different way in which language was used etc. Of course, those things might be paramount to you, but other judges will have different considerations. Accept the fact that you're never going to get all the books you love on to a shortlist and you may not get the book you love to win.
When confronted with the enthusiasms of your fellow judges for a book in which you saw no merit whatsoever, all you can do is be graceful in defeat and say "OK, I can't see what's good about it, but you all love it, so let's allow that on to the shortlist". Don't stab your fellow judges in the back by talking to journalists afterwards - our Booker panel discussions were very civilised and nice, but one of the judges then rushed into print the following day with vicious attacks on the rest of us. So, Jerry Hall, be honourable and fight a good fight.