A key tenet of 6G is a network of networks, upon which sophisticated services can be composed in real-time; this service composition can be realized through decentralized 6G marketplaces of services. These services may include high fidelity real-time holograms, as well as sensitive medical applications, and hence users will have stringent privacy expectations of these services and on the trustworthiness of the constituent service providers and the marketplaces themselves. Rather than specify the details of the required trust in each constituent service provider/marketplace, users will want to specify their requirements through high-level intents on the functionality, price, and trust of their desired composite services. Cross-chain technologies, together with reputation frameworks, provide accountability as an underpinning of trust in such decentralized marketplaces. In this paper, we present an intent-based architecture for cross-chain marketplaces of 6G services, where trust is a first-class factor. Building on our earlier work, we describe several design and implementation approaches for such intent-based service composition integrated with Hyperledger Fabric and Hyperledger Cacti blockchain/cross-chain technologies, and evaluate the comparative benefits of these approaches with respect to key aspects of intent fulfillment and intent assurance. Our work is in the context of UNEXT™, an intelligent networking platform being created at Nokia Bell Labs.