In the second-hand housing sales contract, only the signature of the agent can be considered as authorization. If the agent is legally authorized and has a written power of attorney, then the signature of the agent is valid.

According to the Contract Law of People's Republic of China (PRC):

Article 9 When concluding a contract, the parties shall have corresponding capacity for civil rights and capacity for civil conduct.

The parties may entrust an agent to conclude a contract according to law.