Sapna Maheshwari writes in the New York Times, “In Fake News, Ads Are Costly to Conscience, “, or, online, titled “Advertising’s moral struggle: Is Online Reach Worth the Hurt?”
Some larger companies are now only placing ads in verified whitelisted sites that they check out.
While established ad networks can scan with robots for obviously offensive material (hate speech, and sometimes pornography, especially c.p.) generally they have no way of ascertaining the validity of stories. And up until the election of Trump, fake news sold ads well.
The whole business model for advertising on user-generated content may have been based on misleading material. Facebook and Google, as reported before, are trying to weed it out, at least “voluntarily”, from their ad networks.