My feeling is that the thing that would really rock Google to its core would be a major scandal about ad spend. Like one where they were unambiguously exposed

My feeling is that the thing that would really rock Google to its core would be a major scandal about ad spend. Like one where they were unambiguously exposed - say - channelling all the good leads to people at the start of campaigns and then once the spend was established starting to feed them the shit leads, until they convinced them to spend more money. In short like a Casino that would let people win to give them a taste and then reef them. But of course that's purely speculative and probably that type of thing couldn't be unambiguously proved even if it were true - which it isn't.