This report describes the graduation project for the MSc program Strategic Product Design. The client in this project is Etro Vastgoedzorg, a real estate maintenance company. Etro has a need for having and providing overview on client satisfaction, with the clients being several large housing corporations. To create this overview, the initial research was conducted on which factors were essential for the client satisfaction by performing interviews with several clients. These interviews and further research led to the conclusion that the relationship of both actors can be improved by a different way of working, but first there is a need for making steps in terms of building trust. This led to further research on building trust in inter-organizational relationships and concluded in a measurement model on relational succes factors. To master these factors, a handbook has been made for implementing co-creation in the way of collaborating of the relationship. Both the measurement model and the implementation of co-creation have become building blocks for creating long term relationships, based on mutual goals and mutual trust. The conclusion of this research is that by using the two objects of measuring and co-creating, both actors (Etro and Client) can build actively and cooperatively towards improving their relation.