Just got off the phone with Avis challenging a rental bill that came in higher than the reservation estimate. They were nice enough to credit me the difference. But the issue was the Airport Concession Recovery Fee of 11.11% on a rental with a base rate of $118 and put on the bill as $25.09. That's a fee of about 25%. Avis rep could not define what fees, taxes, and charges the ACRF was based on, and said Avis had no info online where I could read about it. So the mystery is not that the ACRF, but what is actually lumped into the total that it is based on. Seems like the customer is paying a fee on fees.