It is basically impossible to buy second-hand masks, but there is a high probability of buying Sanwu products with pure English packaging. If you put a certificate of certification inside, the mask is not sealed, and many of the insides are stained. (probably produced by small workshops), some pages are marked with test reports, but if you look carefully, you will find that the client and the manufacturer are not correct (some are directly coded or cannot be seen clearly), and you can only buy them with kn95 on Pinduoduo Big brands such as Dengsheng, 3M, Honeywell, and Nanjiren don’t mind choosing because they are OEM and the price is very low. It is best to buy medical protective masks (GB19083-2010) and have a medical registration certificate.
Secondly, when buying masks on Pinduoduo, try to choose individually packaged ones.