I had a similar experience. Is the car rental up the street from Crown bay Marina and if so are they also car dealership?
I rented a car for the day and they charged me for a ding on the rear fender and a ding on the front fender which was clearly marked before I rented car and was charged $800 +
You could see the look on their faces as they thought they got me. At the time AMEX took care of it but I did tell AMEX the we’re ripping us off.