This paper looks at the evolution of large scale mystery shopping survey programmes, which in many instances is being driven by financial institutions. It describes how NOP has reacted to both the development of the market for performance measurement programmes and explains the mechanics of utilising mystery shopping as part of this measurement process. The first part of the paper examines mystery shopping as a means of evaluation. The second part explains how both agencies and clients have reacted to these developments and looks forward to the next generation of mystery shopping surveys. The paper approaches the subject primarily from a practitioners viewpoint. It illustrates how the design and successful implementation of mystery shopping surveys - just as with the more established research methodologies - demands foresight, flexibility and attention to detail - from client as well as agency.