Advertisers assume a percentage of their money is going to be wasted on bots, networks (like Google) assume they will misidentify a percentage of impressions and have to reconciliate the numbers, but also that they'll miss some.
It's very easy to demonise Google and think they stand to benefit from this all, but in reality they are hurt by it as much as anyone else, and if there was guaranteed zero fraud in their network they could raise prices and increase profit.
Advertisers assume a percentage of their money is going to be wasted on bots, networks (like Google) assume they will misidentify a percentage of impressions and have to reconciliate the numbers, but also that they'll miss some.
It's very easy to demonise Google and think they stand to benefit from this all, but in reality they are hurt by it as much as anyone else, and if there was guaranteed zero fraud in their network they could raise prices and increase profit.