Check the car throughly and take loads of photos, they will go over the car with a fine tooth comb at the end. Also photo the windscreen - they found a pin sized mark on the windscreen (1mm max, too small to show up on a wide angle photo) and were going to get me to pay for a new windscreen, when luckily they managed to clean it off (ie it was only dirt in the end). Not a very fun experience - stressful - I have never before had a pin sized mark questioned, let alone one on the windscreen - they told me the windscreen was worth more than the car.