At the last company where I worked we religiously checked the AvData charges against our manifests.
I lost count of the times we were charged for landings we didn't do at places we never went to, on days that we were grounded due to weather etc. We were also charged on a number of occasions for both a take-off AND a landing. That was a favourite trick of theirs! We were also charged for landings at our local aerodrome in WA whilst simultaenously being charged for landings in VIC and TAS.... (Fastest C207 in the world!)
The best one was one of our float planes (Pure float, not amphib) landed on the lake not far from the airport. The number of times we got charged landing fees for that was laughable.
Our accountant would send a copy of the bill back, with corrections and the ammount he believed was payable. They hardly ever disputed it.