Many services are provided in the form of self-service. In self-service, customers simultaneously become the sole producer and a consumer of a service. Using a scenario-based experiment, we examine the psychology of queuing for self-service, and how inter-customer interaction affects service operation efficiency. We assumed that customers could decide how long they would use a service, and that length of usage increases the value of the service, such as in experience stores where customers try out newly released electronic products. Subjects decide how long they will use a service under different conditions of waiting time and social pressure. We found that generalized reciprocity influenced decisions on service time. Customers who had waited for service for long time chose to use the service for long time when it became their turn, and vice versasubjects reciprocated the previous customer's service usage behavior. We also show that the presence of social pressure affects customers' service usage behavior. Under social pressure, customers tend to reciprocate the negative behavior of a previous customer less.