Quality-of-Service (QoS) enhanced service-oriented systems are becoming more important due to the need to support various demands of different application do- mains. Such rising importance and inadequate exist- ing solutions necessitate a finer feature-level develop- ment support that can promote systematic verification of more robust QoS features. Consequently, this paper proposes a systematic methodology to develop versatile or adaptive QoS features in service-oriented systems built for decentralised environments such as peer-to- peer and mobile networks. Keywords: Decentralised service-oriented system, adaptive quality, verification, methodology.