Most white-label arrangements fail in one of three places. The partner pitches past the agency and the client relationship leaks. The build is a demo that works in the meeting and falls over on real data, and the agency carries the blame. Or nobody wrote down who owns the code, who processes the client’s data and who answers the phone when it breaks, and that question arrives on the worst day.
We set those three things out before scoping. We do not contact your client unless you ask us to, and when we are in a meeting it is as your engineering team. We build to production standards, with evaluation sets drawn from the client’s real data. And the contract names the code owner, each party’s GDPR role (usually the client as controller, you as processor and us as your sub-processor), and the support terms after launch.