How do we build models our whole team can trust and defend?

You did not build this model to admire it. You built it to answer a real question, under real pressure, in front of people who will push back. If it only works when you explain it, it does not work. Working with others makes this harder to fake. A teammate opens your file and cannot find where a number comes from. You open theirs and hit the same wall. Everyone nods in the meeting, and no one has actually checked the logic. The fix is not more polish. It is less hiding. Name your drivers. Separate the assumption from the formula. Let someone else break it before a client does. That is the whole discipline.