However, with the existing data set it is not possible to confirm that reciprocity is the main motivation for the observed voluntary payments. Other possible underlying motives for social preferences (“warm glow” (feeling good from contributing to a worthy cause) and guilt (the burden of paying less than one should)) are suggested that appear realistic in the analysed context of an online music store.It may well be that all of them are significant and more specific data is necessary to distinguish between the identified sources. Such an analysis remains for further research. Nevertheless, all three underlying motives – reciprocity, warm glow and guilt – explain the payment behaviour with socially-minded customers who maximise their utility. All three theories are based on a sensitivity parameter (to reciprocity, warm glow or to experience guilt) that is specific to individuals. This can be verified in the payment patterns of frequent customers where four distinct groups can be identified: customers who essentially always pay the minimum, the default, customers who pay significantly more than the average and the ones with a negative time trend.