Don't rent there!
Just rented at their Johannesburg OR Tambo Airport station. Besides the 20% "admin fee" on all the tolls they charged us, a refueling fee and another 6 liters of gas for a fully fueled car (as many others here reported too) were added to our bill. Provided the gas receipts from our whole trip and a screenshot from the mileage, refund still not accepted.
First, support told me that we didn't use enough gas for the KMs we did and therefore the 6 liters were okay to be refueled by them (interesting...). I then escalated this and got a mail from the previously named National Customer Care Manager, neglecting any refund. Her reason was that the gas tank of the cars tend to have air bubbles and therefore I wasn't able to fully fuel up the car. But they were able to then put another 6 damn liters into the car. Imagine how huge this air bubble must have been... DO NOT RENT WITH THEM. Fraud from bottom to top.
Only upside was that we got a brand new Polo, but that's it. Never ever going to rent with them again!