Bargains and rip-offs: A model of monopolistic competitive price dispersion

The main issue in the article is the derivation of a model in which prices can differ in equilibrium, even though the goods are homogeneous and there is asymmetric information in the market. The reason for this price dispersion is caused by consumer heterogeneity. Salop and Stiglitz explain, that “because of differences in preference or ability, some agents perform much better than others in market decisions.” To model this kind of heterogeneity they assign different costs of gathering certain information to the consumers. For simplicity they part the consumers in two groups: The first one consists of low-cost information gatherer and the other group has higher cost to gain complete information. For further simplicity there are just two levels of information: to be completely informed or to be not informed at all. Furthermore the costs to become an informed consumer are fixed. The differences in information in this model regard the locations of the shops. All consumers know about all prices that are in the market, they just do not know where the shop with a certain (the lowest) price is.

The shops on the other hand have complete information about the market. They know about the differences between the consumers and can compute the demand that will occur, when they ask a certain price. So they face a trade-off between higher prices and lower demand. It is important to state why there is a possibility of raising the price and not to loose all demand like it would be in a perfect market. When the rise in price is not too high, it does not pay for the high-cost information gatherer to become completely informed. Their expected loss by buying randomly either in low- or high-priced shops is lower than the fixed cost of gathering the information.

All together this consumer heterogeneity and the fully informed shops can lead to price dispersion in equilibrium, even though the goods are homogeneous and there is the difference in information between the actors.