California Codes, Code of Civil Procedure - CCP, Part 2 — Of Civil Actions, Title 9 — Enforcement of Judgments, Division 1 — Definitions and General Provisions, Chapter 4 — Manner of Service of Writs, Notices, and Other Papers, Article 2 — Manner of Service Generally, Section 684.140

If a provision of this title provides for service by the levying officer of an order, notice, or other paper that runs in favor of a particular person, personal service of the paper may be made by the person or the person’s agent if the levying officer gives permission. The levying officer’s permission may be evidenced by a certificate signed by the levying officer. This section does not authorize the levying officer to give permission to serve a writ or notice of levy. If service is made by a person or the person’s agent pursuant to this section, the cost of the service is not a recoverable cost. Nothing in this section limits the authority of a registered process server provided in this title.