One of the outstanding results of three decades of laboratory market research is that under rather weak conditions prices and quantities in competitive experimental markets converge to the competitive equilibrium. Yet, the design of these experiments ruled out gift exchange or reciprocity...

When alternative market institutions are available, traders have to decide both where and how much to trade. We conducted an experiment where traders could decide to trade either in an (efficient) double-auction institution or in a posted-offers one, which should favor sellers. When sellers face...