I'm not sure about the details of old man Zhang's jewelry. However, if Zhang Laotou's jewelry is a physical store, then we can consider the following aspects to evaluate it:

1. Jewelry quality: you can observe the material, technology and quality of jewelry and judge whether the jewelry is of high quality.

2. Price: We can judge whether the price is reasonable according to the market price of jewelry and the selling price of Zhang Laotou's jewelry.

3. Service: You can judge whether the service is of high quality by examining the service attitude and professionalism of the store.

In a word, if you want to evaluate Zhang Laotou's jewelry, you'd better make a field trip and learn about its jewelry quality, price and service, so as to make an objective and comprehensive evaluation.