Agencies hesitate over outsourced production for one reason, and it is rarely quality. It is the worry that the studio doing the work will eventually be talking to the client directly.
That is a contractual problem, not a technical one, and it is solved by four terms being explicit before the first file moves.
1. No contact, in writing
The production partner never approaches your client, under any circumstance, and has no route to. If your client is not named on the brief at all, the question does not arise.
2. Unbranded delivery
Files come back with no watermark, no studio metadata and no covering note. What you forward is indistinguishable from work produced in-house, because as far as the deliverable is concerned it was.
3. An NDA before anything is sent
Signed first, at no cost, covering the files and the relationship. If a partner treats this as unusual, that is the answer to your question.
4. One named contact
A single person on the production side who knows the account, so the spec does not get re-explained every batch and nobody improvises when something ambiguous comes in.
What this buys you
Capacity you can turn up and down without hiring, at a cost that lets you keep your margin, on work your client experiences as yours. The moment those four terms are in place, the rest is just scheduling.
