How to Measure the Success of a Recommendation System?

Recommender systems are used in a variety of domains, from e-commerce to social media to offer personalized recommendations to customers. The benefit of recommendations for customers, such as reduced information overload, has been a hot topic of research. However, it's unclear how and to what extent recommender systems produce commercial value. It's challenging to create a reliable product suggestion system. However, defining what it means to be reliable is also a challenging task.