Alamo rent a car San Diego FALSE damage charges/ untrustworthy front desk associate San Diego, California

After getting a great deal on carrentals.com I locked in a great price with Alamo for a large van in San Diego. After check-in, I proceeded to pick up the 12 seater van. The van seemed to be in perfect order and I trusted the workers at Alamo had conducted their own inspection. While this wasn't my first time renting a vehicle, it was my first time renting with Alamo. Other companies (enterprise) have inspected the vehicle before departure in order to establish a sense of thoroughness. Needless to say there wasn't an initial inspection conducted, I was late to pick up my colleagues and my sense of urgency and also trust established through other companies didn't trigger a thorough inspection on my behalf.
I drove the Van to the destination and parked the car for the whole day at the hotel. The next day I drove back to San diego and returned the car on the following day. Upon entering the Alamo lot the drop off attendant inspected the vehicle with thoroughness that was not conveyed in the same manner when i first picked up the vehicle. The inspector noted a small dent on the bumper that clearly was there previously and iterated that it would need revision. I was sent to the front counter to check out. I then came in contact with Jonathan who agreed that it was probably a dent from a previous renter and that charges would no be pursued due to how small the dent was.
While i did feel assured, I also felt they were being slightly untrustworthy so I called their contact center and asked if there was a claim made. During multiple calls for two weeks they assured me that everything was fine. Today, I received a letter to contact their damage recovery unit. The dent that wasn't a problem is 450 dollars.
I am writing this because I am disappointed in my rental experience with Alamo. Despite the charges which I am currently disputing It is troubling that Alamo colleagues deceive their customers through false appeasement. If there had been a strong initial inspection that mirrored the return inspection then I would feel less inclined to question their later claims. Also, wouldn't a strong initial inspection create a feeling of genuine care for the renter? I know without a doubt that the dent on the vehicle was there before I rented the van due to securing the vans location throughout the trip. I only wish I could have understood my error in not inspecting the vehicle with shrewd scrutiny. It is clear that I probably wont rent from Alamo ever again due to the untrustworthy business practices exercised from this company.