Incentive mechanisms are crucial in large-scale decentralized wireless mesh networks, as they help promote network stability and participation. The core of incentive mechanisms is to accurately measure the traffic shared by each participant and distribute the network income fairly. However, the lack of a trusted third party can bring about security and performance issues, such as non-real-time incentives and potential fraudulent activities during the settlement process. Motivated by recent developments in decentralized consensus mechanisms and cryptography, this paper proposes PoT, a new proof-of-traffic incentive mechanism for decentralized wireless mesh networks. We aim to construct a Blockchain Layer-2 consensus to address automatic traffic usage determination and settlement. PoT enables participants to reach a global consensus by randomly listening to a small fraction of the traffic communicated between each other. We leverage Verifiable Random Function to randomly select listeners, apply equilibrium analysis to the voting game between participants and demonstrate that PoT satisfies truthfulness and weak budget balance. Compared to existing methods, our approach does not require frequent signatures and is based on existing traffic. Furthermore, our mechanism incurs communication overhead on an active network of less than 5%.