The Law of Agency is fairly well established, including:

Liabilities in Agency Law

Both the principals and agents are responsible for actions performed under the agency law. The liabilities may come about in various circumstances:

• Liability of the Principal: Generally, the principal is liable for actions performed by the agent within the scope of the authority. This includes contractual liability and third-party claims.
• Agent’s Liability: The agent may be held personally liable if they act outside the scope of the authority vested in them, are fraudulent, or do not indicate that they are acting on behalf of a principal.
• Third-Party Liabilities: Where an agent falsely represents that they have authority when they do not, third parties may sue the agent or the principal, depending on the situation.

It would be interesting to see, in a case like this, whether the courts decide that there was an agent with agency and, if so, exactly who the agent was. If there was an agent and agency according to the Agency Law, it seems the court would have to recognize the ‘AI agent’ as a legal entity, distinct from Meta, or hold Meta responsible as the agent, as Meta ran the ‘AI agent’ and contracted with the seller for its services.

I wonder how long it will be until this is put to the test in court by some disgruntled purchaser who is out more than the cost of a keyboard.