Growth in the metaverse has been significant in recent years, aided by the robust communication capacities of the 5G network. Moving into the 6G era, integrated sensing and communication (ISAC) services are regarded as a potential solution for controlling avatars in the metaverse, because ISAC can enable users to have all-pervasive sensing capabilities at all times without needing additional equipment. However, current research primarily delves into the technological aspects of ISAC under the presumption of these sensing services being handled by centralized entities, such as corporations or organizations, while considerably less attention has been given to the potential issues inherent in such centralized control, including problems of privacy and the risks from monopolies. In light of these gaps, our paper introduces a novel framework for implementing blockchain-based ISAC services in 6G networks. Recognizing the associated challenges and possible risks with our proposed framework, we provide an interactive process featuring appropriate solutions. Moreover, this paper further evaluates the capacity and performance of our theoretical framework through a case simulation based on the real-world distribution of base stations. Furthermore, we conclude the limitations inherent within our proposed blockchain-based ISAC services and provide a list of relevant and consequential future research topics.