Mobile ad hoc network (MANET) assumes that all mobile nodes are cooperative. However, this cooperation cannot be assured due to MANET features such limited resources of nodes and network openness. Since mobile nodes are constrained in term of energy, nodes may behave selfishly by refusing to forward packets for the benefits of other nodes in order save their energy. Credit-based schemes and reputation-based schemes have been proposed to deal with selfish nodes. Although these schemes can stimulate the cooperation of selfish nodes, they fail to detect smart selfish nodes dropping packets at a low rate in order to avoid being considered as selfish, while at the same time to use network resources freely. In this paper, we address the problem of smart selfish nodes by proposing a new adaptive credit-based stimulation scheme, called NADS. In NADS scheme, each node maintains a credit-account for each neighbor. The price and the reward of each packet relayed depend on the cooperation level of nodes. The proposed scheme is designed to perform in a fully distributed fashion without involving any central authority. The simulation results show that NADS scheme reduces the selfish delivery ratio and the exclusion times of selfish nodes in comparison to OCEAN an EAACK scheme.