In common-value auctions an auctioneer can enhance the seller's revenue by making all the private information she possesses regarding the item's value available to bidders before the bidding takes place. This prediction relies on the bidders being rational. On the other hand, if bidders have naive beliefs regarding the item's value and suffer the winner's curse, an auctioneer would maximize the seller's revenue by not making any information publicly available to bidders before the bidding takes place. In other words, conditional on the auction mechanism, an auctioneer only affects auction results by her choice of public information disclosure policy. In private-value auctions an auctioneer has a limited or no role to play in determining auction outcomes, and thus, conditional on the auction mechanism, the number of bidders, and the distribution of private values, auctions results should be invariant to the presence of an auctioneer. In reality, most auctions (such as most English auctions) are neither strict common-value auctions nor strict private-value auctions but have elements of both types. However, to the extent that an auction exhibits some common-value elements to it, one should observe auctioneers making all information about the item for sale publicly available to bidders before the auction starts, and auction outcomes only altered as a result of this information.

This dissertation tests the above predictions in three settings: common-value auctions and private-value auctions in a laboratory environment, and English auctions in a field setting with the presence of a professional auctioneer. Although for private-value auctions the results are largely in agreement with theoretical predictions, the other two studies demonstrate that contrary to theory, or intuition, the mere presence of an auctioneer can lower seller's revenue by making bidders bid more conservatively. I denominate this effect the auctioneer effect". A structural level-k model of reasoning fitted to the common-value auction data confirms that players apply more thinking steps to formulate bids in auctions with the presence of an auctioneer, and bids are closer to Nash equilibrium predictions, which naturally hurts the seller.