This research aims to analyze the implementation of the principle of good faith in endorsement agreements between online shops and influencers. This principle requires each party to act honestly, transparently, and fulfill their obligations in accordance with the agreement. However, in practice, endorsement agreements often face obstacles, especially in meeting the agreed promotion schedule. This research uses an empirical legal method with a descriptive qualitative approach. Data were obtained from interviews with online shop owners, literature studies, and document analysis of endorsement agreements. The results showed that the implementation of the principle of good faith was not optimal, especially at the post-contract stage. Influencers postponed uploads several times without clear certainty, causing uncertainty for online shops in their marketing strategies. The absence of a penalty mechanism in the agreement left online shops without legal protection against such delays. This research emphasizes the importance of drafting more detailed agreements and ensuring transparent communication between the parties to ensure that the endorsement agreement runs in accordance with the principle of good faith. It is hoped that the results of this study can provide insights for online shops and influencers in designing endorsement agreements that are clearer and beneficial for both parties.