Advertisers by media (ad space). That ad space is usually defined by parameters or attributes. It could be based on characteristics of the user, like demographic or audience (like car shoppers), but often has other criteria of content attributes, and that can be negative attributes, like no ad space on porn sites or on pages where my direct competitors also have ads. So when Google misrepresents that ad space to the advertiser that had those specific parameters on the deal, it's a problem.