There is a high potential of creating new and market-ready services for the Internet of Things (IoT) community by enabling end-users to make their resources inside the end-user environment available to others. Thus, end-user friendly service platforms facilitate the process of designing and configuring new local and cooperative services. However, decentralized networks of end-users acting as service providers enable the risk of uncontrollable behavior and trustless activities. Blockchain technology coupled with smart contracts now gain popular attention by providing benefits of data immutability and process automation in open or closed communities. This research summarizes several blockchain-based IoT approaches, concluding with their benefits and limitations. Besides them it proposes an optimized and decentralized IoT marketplace consisting of end-user friendly IoT service platforms, forced by a synergy of trust, blockchain and smart contract elements. To highlight the benefits of this synergy, two smart contract use cases (based on Ethereum) in the IoT marketplace are presented.