What characteristic does NOT enhance the effectiveness of a custom GPT?

A characteristic that does not enhance the effectiveness of a custom GPT is obtaining real-time feedback from users. While feedback is undoubtedly valuable, especially for iterative improvements in generative models, it is not a direct enhancement feature of the model itself.

The other options involve strategies that directly contribute to customizing and refining the behavior of the GPT. Detailed instructions for behavior help in tailoring the model's responses to meet specific needs and context. Uploading reference files like style guides provides the model with a framework within which it can operate, ensuring consistency and alignment with desired outcomes. Testing the model with sample inputs enables developers to observe its performance in action and make necessary adjustments to improve its functionality. Therefore, while real-time feedback is important for ongoing improvement, it is not a characteristic that inherently enhances the custom model's effectiveness.