This paper analyzes the impact of misbehaviour on QoS provisioning in wireless mesh networks. Misbehaviour occurs when a network participant decides not to cooperate. Since cooperation is fundamental for distributed environments such as mesh networks, misbehaviour can be a serious threat to them. In this work, the authors focus on the IEEE 802.11 EDCA medium access function which provides QoS in mesh networks. Simulation studies have been performed to determine what realistic forms of misbehaviour can occur and what their impact is. From these results the most beneficial forms of MAC layer misbehaviour in multihop mesh networks are derived.