Can my mother be served if she did not answer the door?

Depends with what she was served.

You bring up two different issues. The first: can she be served without opening up the door? Yes. A process server no longer has to actually touch a person with the papers in order to serve them. If they knock on the door, and your mother is aware of who they are and what they want, and they are aware of who she is, she can be considered served even if she does not open the door. The second issue revolves around the duplicitous nature of the person serving her. In CA the State has standards for professional process servers, I believe pretending to be a pizza delivery falls outside of those standards.

The regulations in regards to personal service of legal documents are that the person being served is within normal speaking distance; the person is identified as the person being served; inform the party they are being served; give the documents to the party, if the party refuses the documents-they may be left in their presence. If your mother confirmed that she was the party being served through the door, then she may be considered served.

Legal? If they file a Proof of Service with the court claiming she was served, and she doesnt timely file an Answer or responsive pleadings, they will enter a judgment by default. The proper question is what can she do now? She could try to contest service by filing a Motion to Quash, if she has valid grounds for doing so and can prove what she alleges as improper service. All that would do if she were successful is make them re-serve her, an additional cost they will assess against her in the case. If plaintiffs claim is valid, either negotiate a settlement or defend the case. If this is small claims court and she contests the claim, file an Answer and go to the trial and defend the case. If this is Superior Court, seeking large damages, then file responsive pleadings, raising all possible defenses. File motions, demurrers, or whatever is appropriate, with whatever admissible and credible evidence and facts are available for legal arguments. Not exactly a do it yourself project in court for someone who does not know how to effectively represent himself against a professional attorney seeking judgment against you. If she doesn't know how to do these things effectively, then hire an attorney that does. If serious about hiring counsel to help in this, and if this is in SoCal courts, feel free to contact me.

No, she has to have been served in person. If the door was never open, she wasn't served.

That is not proper service as personal service. Requires documents to be personally given to an individual.