Enterprise Car Rental Pre-existing damage scam Milwaukee Wisconsin

We rented a car from our local Enterprise location.  When we picked up the car the Enterprise employee did a very curosry examination of the lower portion of the car with a wand of some sort.  They had just moved their location and there was very little light.  When we got the car into sunlight we noticed quite a bit of damage to the vehicle.  I took pictures of the damage with my cell phone within 20 minutes of having picked up the car.  When we returned the car today they said we were liable for the damage despite the fact that I had picture dated from the day of pick up.