How Google Reaches 90% Market Dominance

Google had an information advantage about the identity of the user loading an impression on a page at a particular time. If Google happens to know that nobody else knows the identity, they might bid a lot lower than they would have otherwise and still win. But my understanding is also they can decide to share some information with some friends but not with others. And if you don't, you might end up stuck with a bunch of impressions that are of bots rather than real people.