Sustainable urban development has come to play an essential role in establishing and growing future sustainable cities, or smart cities, which are urban areas that have an optimum carbon footprint, are nature-friendly, and are smart enough to enhance energy efficiency. This study is based on qualitative research in which data were collected from interviews with real estate development specialists. The interviews were addressed to a total of 30 real estate developers from Romania between July and December 2022 and were conducted using the Zoom interface. The aim of this research was to analyze whether familiarity with the smart green concept influences the decision to implement the IoT on a large scale at the organizational level through the perception of specific determining factors in choosing the development of green building projects considering the operational costs. The results revealed a significant indirect effect of green building knowledge on large-scale IoT implementation through the mediator of the perception of operating cost factors, supporting our hypothesis. The direct effect in the presence of the mediator was not found to be significant anymore. Hence, there is full complementary mediation by the perception of operating cost factors on the relationship between green building knowledge and large-scale IoT implementation.