In this paper, we propose a new scheme to detect misbehaving nodes that violate their contracted bit rate in the context of wireless ad-hoc networks. To achieve this, we use our DCF-MB access policy instead of the well known DCF protocol. The DCF-MB approach ensures a fair time occupancy of the shared channel among competing nodes. Using our DCF- MB access scheme, we derive analytically the expected useful occupation ratio of the channel when all the nodes respect their contracts. This value is used as a reference to detect misbehaviors inside the network. We show through simulations the efficiency of our proposal that ensures fair bandwidth sharing, enabling thus the detection of misbehaving nodes. We also evaluate through simulations and analytic analysis the effectiveness of the system in estimating the useful channel occupation and improving the network performance.