I don't have to sign a car purchase contract to have legal effect: 1. If someone is authorized to sign the letter for you within the authority of the agent; Or you know that others have signed the cooperation agreement in your name and don't deny it, then the signature is valid and the car purchase contract is valid. 2. If someone else signs on your behalf without authorization, beyond the scope of authorization or after the authorization is terminated, the signature of the agent is valid and the cooperation agreement is valid after your ratification. Article 502 of the Civil Code, a contract established according to law shall come into effect upon its establishment, unless otherwise provided by law or agreed by the parties. In accordance with the provisions of laws and administrative regulations, if the contract should go through the approval procedures, such provisions shall prevail. If the failure to go through the formalities such as approval affects the effectiveness of the contract, it will not affect the performance of the obligation clauses such as approval and the effectiveness of relevant clauses in the contract. If the party that should go through the formalities for approval fails to perform its obligations, the other party may require it to bear the responsibility for violating its obligations. The modification, assignment and dissolution of a contract shall be subject to the provisions of laws and administrative regulations, and the provisions of the preceding paragraph shall apply and shall be subject to approval.

Legal objectivity:

Article 161 of the Civil Code: A civil subject may carry out a civil juristic act through an agent. In accordance with the provisions of the law, the agreement of the parties or the nature of civil legal acts, civil legal acts that should be implemented by themselves shall not be represented. Article 162 of the Civil Code: A civil juristic act carried out by an agent in the name of the principal within the scope of agency authority is effective for the principal.