How do rental car companies make any money?

The rental car company by my bodyshop has about 10 people working in there office and rents cars from $20-$40 a day. How do they make any money?How do rental car companies make any money?
My profession is accounting, and trust me, car rental places make money. Sure, they will advertise $20 - $40 per day, but look at some of the upgrade rentals. 2 years ago, I rented a Hertz Shelby Mustang for 6 days and paid over $1,200. It was totally worth it. I had a blast with the car. If you figure that the car costs Hertz about $600 - $700 per month, the car starts to contribute to the margin after the 4th rental day per month. If they rent it for 20 days in a month, they take in $4,000 in revenue.





Most rentals are for mid-size cars to business travelers who charge the expense with a company credit card. Often, it will cost $70 - $90 per day just for the car without add-ons.





There are also other charges that are tacked on when you rent, such as supplemental collision and personal property insurance that many renters select, but often never use.How do rental car companies make any money?
I was told by a friend that works for a popular rental company they make money when they sell the vehicle at the end.