You can sign the purchase contract on your behalf. The purchaser signs a written agency contract with the entrusted agent, which clearly states the agency matters, the authority of the agent and the personal information of the agent, and the entrusted agent can sign the purchase contract on his behalf.

legal ground

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 A civil juristic act carried out by an agent in the name of the principal within the scope of his agency authority is effective for the principal.