Second price: Usually famous brands are not discounted. If the merchant bargains with you, you should pay attention to the severe discount, which is likely to be a fake.
The third mode: some imitators are just fooling around with a brand and model. You can check whether this model is available on the Internet, and it is available in official website.
The fourth certificate: the manufacture of brand-name spectacle frames can only be sold in optical shops with special certificates. Without a certificate, it is fake, with a certificate, it is true and easy to recognize.