The third and perhaps most important reason why tipping should be an area of research activity relates to the inherent uniqueness of the behavior. Tipping is one of the few areas of the economy where the exchange is dictated by informal rules of custom rather than explicitly stated procedures. While there are certainly other instances where informal rules dictate the exchange (e.g., the interchange at a swap meet (Belk, Sherry and Wallendorf 1988; Sherry 1988) or the purchase of a used car), these tend to be less prevalent than tipping. For most goods and services, the rules of exchange between buyer and seller are clearly known by the participants. Prices are ordinarily stated explicitly and the time and method of payment are known. In contrast, the custom of tipping is guided by informal rules and norms. While suggested amounts of tips and who should be tipped are indicated in books on etiquette (Post 1975) and on tipping (Star 1988), these are particular individuals' perceptions of the custom and many people are unaware of these sources.