I do not know which community guidelines I have violated and got a 7day ban. 
It
was about music￼ so I have a hard time understanding what they didn't
like. 
I am left without clue.

The post is a little hard to understand. Are you quoting a lyric poem by Jiang Kui? If so, it could be that they felt that you didn't correctly cite the reference. I made some corrections, but I'm not sure about the quoted material.  Here are my corrections:
                                         
 I tried to sell a flute, but even though it was priced AT 500 RMB, there were still many people who asked FOR a discount, so I decided not to sell it. I believed that the price was fair because I had seen this brand (LeBrown) on other websites which were priced at $100 USD or more. Maybe because I like Jiang Kui and his lyric poems I find the flute more valuable than others do.