The offline market selling second-hand mobile phones is local to Yuncheng. You can go to Dongxing Road and walk south to the crossroads, where you can buy and sell second-hand mobile phones (it's close to Dongxing Times Square, just ask anyone). If it is not local, you can go to Huaqiang North.

On the platform of selling second-hand mobile phones online, you can choose the excellent product pat, which is a vertical platform.

Supplementary information:

Dongxing Times Square-Baidu Map