The reason for this is the following：

1 and 9 1 versions of second-hand houses are older. 9 1 version of the second-hand house has been more than 30 years, and the house is aging and damaged, which needs more maintenance.

2. Version 9 1 of second-hand house is out of date. 9 1 version of the second-hand housing unit design is not reasonable enough, the space utilization rate is low, and the living experience is not good.

The supporting facilities of 3.9 1 version of second-hand houses are backward. The 9 1 version of the second-hand house has imperfect peripheral facilities and inconvenient transportation and shopping, which affects the convenience of living.