In most markets for consumer goods, there do not exist identical products from the viewpoint of consumers. Even if physical properties are hardly distinguishable, branding may achieve that products are differentiated. A number of questions ensue as to how to apprehend product differentiation. How do consumers perceive products and services? To what extent do different consumers share the same perceptions? How similar are the demand curves of various individuals? Do consumers care for variety? The answers to these questions, and hence the modelling choices of the analyst, depend on the nature of the products or services under consideration. Think for instance of the car market, which has been the object of a number of empirical studies. Here, the assumption that consumers buy a single car, but that the population of consumers has heterogeneous tastes, is a natural assumption to make. For other consumer goods, neither discrete choice nor unit demand are natural assumptions to make. If you think of beer or carbonated soft drinks, the discrete choice assumption is often an appropriate assumption to make but consumers not only differ in their brand preference but also in their individual demand curves. In the case of wine, we believe that neither unit demand nor discrete choice are good approximations of actual consumer behaviour and therefore, are bad modelling assumptions: a large share of consumers actually enjoy some variety and buy variable amounts of quantity.