They don't. They request some documentation, verify some facts that they can correlate other sources, but mostly they rely on the fact that intentionally lying

They don't. They request some documentation, verify some facts that they can correlate other sources, but mostly they rely on the fact that intentionally lying in the declarations is a crime - they can trust most reports, audit some, and penalize those violators they caught as a deterrent to make it not worth the risk to lie.