Just bought a maxi cosi pebble car seat which is a couple of years old and (according to the seller) has never been in an accident, for DS3 (due in June). Then remembered that you're not supposed to buy car seats second hand. Anyone know why this is? Is it just because you can't be sure if it's been in an accident, or for other reasons? Seems they are £145 new and would only get used for 12 months or so.