We propose a decentralized conceptual marketplace model for IoT generated personal data. Our model is based on a thorough analysis of personal data in a marketplace context, with specific focus on the challenges presented by commercializing IoT generated personal data. Our model introduces a novel perspective on the commercialization of personal data for a marketplace context via risk evaluation and a data licensing framework. We have designed our model to be centered around protecting the privacy and data rights of data generators through model components that effectively assess and modify transaction risks, and formalize transaction agreements by establishing rights of data use and access between buyer and seller. Our model could serve as a blueprint to inform the implementation of a personal data marketplace that respects privacy and ownership.