I can't guarantee that hiring a lawyer will make Alamo back down, but I can guarantee you that Alamo will take your defense a lot more seriously if you do hire a lawyer. I'm guessing that your rental agreement has an attorney's fee clause, so your lawyer can not only argue that you're not liable for this scratch, but can also argue that Alamo is responsible for your legal fees. That itself may make Alamo think twice about picking a fight with you.
Avvo doesn't pay us for these responses, and I'm not your lawyer just because I answer this question or respond to any follow-up comments. If you want to hire me, please contact me. Otherwise, please don't expect a further response. We need an actual written agreement to form an attorney-client relationship. I'm only licensed in CA and you shouldn't rely on this answer, since each state has different laws, each situation is fact specific, and it's impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue.
You can fight with Alamo but, short of being awarded your attorney's fees, you loose. If it is reported as damage occurring when the car was legally parked it will be on your comprehensive coverage and, probably a lower deductible.
Your call, and probably your money.
Never pick up a rental in the dark.
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