Since you were the person who rented the car and signed the rental contract you are responsible for the damage to the car when you have no insurance. If you want your brother to pay that is another issue because if your brother was not an authorized driver the rental car company will not be looking to him for reimbursement as well.
DISCLAIMER: David J. McCormick is licensed to practice law in the State of Wisconsin and this answer is being provided for informational purposes only because the laws of your jurisdiction may differ. This answer based on general legal principles and is not intended for the purpose of providing specific legal advice or opinions. Under no circumstances does this answer constitute the establishment of an attorney-client relationship.
Upon renting the car you assume liability. Contact your insurance company.
contact your insurance company. if they have an exclusion see if your credit card company covers it. Some do. If they don't you may be paying out of your pocket. Good luck.
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If the rental car company sues you, you will probably be on the hook for damages as the other attorneys have said. However, you may be able to add the person that hit the car as a third party defendant to the lawsuit and seek indemnifcation if you wind up having to pay, since he did actually cause the damages through his negligence. However, if he does not have any assets from which to collect a judgment, you would probably just be wasting your time and money. I do however, think the legal right to sue him for indemnifcation does exist in this case, even if it's not practical.
The above is not legal advice. That can only come from a qualified attorney who is familiar with all the facts and circumstances of a particular, specific case and the relevant law.
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