The methods for identifying inferior protective films include:

1. Observe the appearance of the protective film. A good protective film should be flat, and smooth, without bubbles, wrinkles, or damage.
2. Smell the protective film. If there is a pungent odor, it is likely made of inferior materials.
3. Feel the protective film. A good protective film should be smooth and soft, without scratches or color fading.
4. Check the quality certificate and testing report of the protective film to understand if its performance and quality meet the requirements.
5. Observe the condition of the protective film after using it for a period of time. A good protective film should be able to maintain its performance and appearance durably.