Abstract This paper presents a credit-based incentive mechanism for delay tolerant networks which enables device-to-device data exchange without the support of traditional Internet service providers. The solution uses a utility function that represents the monetary value of a given data message during its journey in the network, and a buffer management optimization algorithm to prevent selfish behaviour among nodes. Virtual banking relies on an off-line central trusted authority. The paper introduces the concept of isotropic deliveries in delay tolerant networks which uses binary spray and wait forwarding strategy. Simulations with the IEEE 802.15.4 standard show the proposed incentive mechanism preventing selfish behaviour and guaranteeing more extra credits to the end-user.