Today, Cloud services are mainly traded on provider platforms such as on Amazon's EC2 On-Demand marketspace. Thereby, consumers and providers neither negotiate the price nor the characteristics of the services. The recent years underpin a trend to more dynamic Cloud markets. So e.g. the Cloud provider Virtustream released a revenue model where consumers are charged based on consumed μVMs while Amazon extended it's spot market with spot blocks and spot fleet management. Hence, multi-round bilateral negotiations are a promising approach for trading Cloud services on future Cloud markets. Such negotiations are based on an alternating exchange of offers and hence, they are termed Bazaar-negotiations. Specifications such as the WS-Agreement Negotiation - which is maintained by the Open Grid Forum - foster the development of Bazaar-based markets. To ensure integrity and transparency of negotiations with untrusted negotiation partners - which is a precondition for the adaption of Bazaar-based Cloud markets - blockchains are a promising approach. In this paper we introduce a concept of a blockchain for Bazaar-negotiations whereby we assume that the offers exchanged during negotiations follow the structure defined in the WS-Agreement Negotiation specification. We implemented it within a CloudSim based simulation environment which is able to simulate such Bazaar-based markets to show its technical feasibility.