personally i think best bet is to talk to manager

that you were not asked to confirm decline insurance coverage at the time of rental, and see if they will let you off the hook. not too good if box "liability damage" checked. you're at their mercy. you can tell them you will spread the words if they treat you like a junk. but like everyone else (this one), sometimes you'll have to pay for the hard lesson and this time it's $450.