Counting Fuel Does Not Work
Problem here is that the same guys who are smart enough to manipulate all load data on all of the ends of your cargo run, are also smart enough to create fuel consumption data to match the expectations. This on top of the fact that some of the fuel you pay for never makes your fuel tank but gets sold off by the mechanics (traditionally in charge of refuelling) in cooperation with the fuel truck drivers.
Nothing beats having honest, non-corrupt (and well paid) flight crew. One well run operator in the area gives the pilots the right to do re-weights at any time (even if it delays the flight) and confirm that what is on the manifest is the correct number. If discrepancies are found, the customers (who are normally providing the load and manifest) are fined US$ 20.000 for the 1st offence, and contract termination for the 2nd.