 Not nearly as much as advertising and marketing departments say. One paper we cited in those episodes is by the Berkeley economist Steve Tadellas and two co-authors. They used data from eBay. Here's Al Roth again. Apparently eBay used to buy ads on Google search on the name eBay. So if you searched for eBay, you saw not just eBay's website, but you also saw an ad from eBay.