A bombshell trade report lands next month which will reveal whether US advertising agencies accept rebates from media companies, and whether those agencies are transparent about disclosing them and passing them back to their clients.

The report, commissioned by advertiser trade body the Association of National Advertisers (ANA), is set to be more “explosive” than many people in the industry were prepared for, these sources say, because it will lay bare the practices media agencies use to make hidden margins on their advertising buys. A previous report on the same issues from the ANA, published in 2012, was widely ignored.

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