Misinvoicing is the most-documented trade-based technique because it leaves a paper record that can be checked against an independent one. If an invoice says a consignment of pumps is worth two hundred thousand dollars and the market says the same pumps are worth two million, the difference has gone somewhere, and the direction of the error tells you which way value moved.
Global Financial Integrity’s published methodology, and the mirror statistics approach it uses, treat systematic gaps between paired country reports as the aggregate footprint of this behaviour.