Secure and transparent cooperation between Internet of Things applications and edge computing are crucial for the full realization of smart city technologies. To reduce the processing load of Internet of Things (IoT) tasks, devices with limited resources might use fog computing. For the security of IoT data, fog and IoT must authenticate with each other, and for fog services to be monetized, the fog service ecosystem must be improved. But, fog nodes could intentionally or unintentionally fail to reliably respond to Internet of Things (IoT) queries. Establishing trust amongst fog nodes is crucial in the public decentralized Internet of Things (IoT) fog ecosystem. A blockchain-based system is presented in this paper that (1) optimizes the revenue generation from fog-IoT mutual authentication services (2) guarantees that fog nodes are honest by conducting service audits, and (3) uses incentives and penalties to deter dishonest behavior and encourages fog nodes to be honest.