Agree the definitions before building the dashboard
The reason two reports disagree is almost never a broken query. It is that "active customer" means one thing to sales and another to finance, or that revenue is counted at order date in one place and at invoice date in another. Building more dashboards on top of undefined terms multiplies the problem.
So the first deliverable on a BI engagement is usually a written definition of each core metric — what it counts, what it excludes, which system it comes from, and who owns it. It is unglamorous work, and it is what makes the numbers trustworthy enough to act on.
Once definitions are settled, they live in version-controlled transformation logic rather than being re-implemented in each dashboard. Change the definition once and every report follows.