It is common to hear that big or small organizations are moving to cloud computing for its scalability and cost savings. But, how do you decide which cloud provider to trust? Trust is a vital factor, especially for service oriented systems in the area of Information Technology and Security. Several issues have been raised by enterprises and individuals concerning the reliability of the cloud resources. In cloud computing, trust helps the consumer to choose the service of a cloud service provider for storing and processing their sensitive information. In this paper, a methodical literature analysis of trust management and existing trust models is presented to evaluate trust based on various QoS parameters. Key research issues and future research directions in existing literature are also suggested.