Auctions and adverts

I’m slowly making my way through the back episodes of the podcast Linear Digressions.  Normally it’s about machine learning, but there are a couple of episodes (one big episode chopped into two) about auctions.  As in, how do eBay and Google make money (not the same way) and which is better?

There is some interesting stuff on competing or aligning incentives, hiding or revealing information, optimising global happiness across all actors and so on.