@tarponchik's advice about rental cars is good. I've had many similar experiences in Panama. They've charged me $150 bucks for a tiny door dent that I'm sure was already there. Once I got rear-ended (other driver's fault). The rental car company charged me for the damage, even though I had the police report showing the other person was at fault and had their insurance info. They told me I could contest the charges in traffic court a month after my planned departure. In Latin America, the car rental companies understand that the kind of have you over a barrel.