The relationship between brands and their media suppliers has been in the spotlight since the start of the year when one of the world’s largest advertisers attacked agencies for being untrustworthy.

Marc Pritchard, the chief marketing officer at Procter and Gamble, said the media supply chain was “murky at best and fraudulent at worst,” in a speech given at a digital marketing conference, although he added that P&G was partly to blame for not scrutinizing agency contracts closely enough.

The problem is complex, ranging from how much online adverts are actually seen by anybody and the definition of digital ad measurement, to “hidden” rebates, where media agencies don’t disclose or return savings to their advertiser clients.

It also includes marketers’ concerns about their ads appearing on websites or next to unsavory content, including brands like HSBC, L’Oreal and U.K. retailer Marks and Spencer which pulled adverts from YouTube after some of them appeared next to extreme content back in March.

The latest twist in the tale came last week when Uber filed a lawsuit against mobile ad agency Fetch, claiming that the company billed it for fake clicks on its online ads. Fetch has denied all allegations.

Now chief marketing officers (CMOs) will be aiming to take much more control of where their brands appear, according to industry expert Liz Miller, senior vice president of marketing for the CMO Council, a U.S. business network.