Bidding behavior in experimental auctions with positive and negative values

We test for consistency between bids from endowment auctions that allow positive or negative bids for an exchange between two items, and bids from prior full bidding auctions for the same items. Results suggest that positive WTP bids in the endowment auction are demand revealing but subjects overbid (in absolute value) their negative WTA values. WTA bids were lower in a random nth price auction than in a 5th price auction.