As auctions are becoming the main mechanism for selling advertisement space on the web, marketing agencies specialized in bidding in online auctions are proliferating. We analyze theoretically how bidding delegation to a common marketing agency can undermine both revenues and efficiency of the...

We present an empirical investigation of the role of marketing agencies in Google's online ad auctions. By combining data on advertisers' affiliation to marketing agencies with data on bidding in ad auctions, we analyze how changes in the concentration of clients in the same industry under the...