Third-party engagements — when to commission, how to oversee

External testers are not a substitute for an internal program; they augment it. Use them when one of three conditions holds:

Capacity: too much testable scope for the internal team in the cycle.
Capability: a specific domain (multimodal, agentic, specialized model) where internal expertise is shallow.
Independence: a regulator or audit requirement explicitly demands an external test.

Selecting

Five criteria, weighted in this order:

Methodology fit: Their published methodology should be compatible with this framework’s structure (charter, ROE, three-tier reporting). Ask for sample (sanitized) deliverables.
Practitioner-level personnel: Who actually runs the engagement, not who pitched it. Resumes of named personnel, not the firm.
Domain match: Recent comparable engagements at peer organizations.
References that you call: Not the references the firm provided — adjacent contacts.
Commercial terms: IP indemnity, deliverable ownership, scope-change discipline, NDAs.

Engagement scope ties to the ROE (your ROE, not theirs).
Deliverables in your formats.
Right to publish (yours), right to anonymized reference use (theirs, capped).
Personnel substitution requires approval.
Tools used disclosed in advance (some clients prohibit certain commercial scanners).
Confidentiality and breach handling tied to your standard.

You remain accountable. Concretely:

A designated internal owner attends standups.
Internal review of evidence before findings are accepted.
Re-perform a sample of findings (chapter 8 quality bar applies).
Drive the compliance-traceability section yourself, even if the external tester drafts it.

Accepting reports without internal review, then being unable to defend them at audit.
External tester’s report uses commercial tool output verbatim. Re-frame in your methodology.
Engagement runs longer than scope; budget slips. Set hard checkpoints.