You know that Nielsen is a multi billion dollar company with a staff of 40k and one of the most trusted information companies around right?
Providing trust worthy information is what they do, they are not some type of monopoly, people pay for their services cause they are trustworthy if they weren't they would get left in the bushes.
All these numbers they report are directly tied to certain section of labels revenues, public companies that own radios are not trying to fukk their money up, it's not hard to calculate if they they are faking it. You either have some person with no life expose them, their competitors, regulators, the IRS or someone else.
The thought of a major public company paying another large public company millions of dollars to fukk up their money.