Trust is as significant a factor for successful online interactions as it is in offline communities. Trust is an important factor that is used as a criterion for service selection. There is a need to know information about services and service providers to establish trust and identify their trustworthiness. Most trust studies focus on trust establishment for services without clearly identifying trust information for services and service providers. Services and service providers traverse many domains with different properties and requirements. Identifying a unified trust information (trust metrics) for such an open environment is a challenge. This paper proposes a unified trust metrics classification for services and service providers. The proposed trust metrics can be extended and used in an open environment or within specific domains to establish trust for services and service providers.