You really can't go to those so-called big music shops to learn piano. The musical instrument training in those music shops is incidental, not the main business. If you want to learn something, you should go to a special training center.

I know a training center, you can ask about it. Nantong is training music every day, and the guitar teacher there is quite responsible. There is a teacher Zhu who is very good at classical guitar. There is also a teacher named Xu, whose major is pop and electric guitar. He used to arrange music and improvise everything. Last time I listened to their guitar audition class, the teacher spoke very seriously. You can search online if you are interested. They have videos of students.