I ask what decision they'll make with it, and what they do today instead. Nine times out of ten the dashboard is a proxy — they're doing a manual reconciliation every month and they want the answer, not the chart. At [company] I had a request for a spend dashboard that turned out to be one person exporting three systems into Excel every Thursday to answer a single question a VP asked in a Monday meeting. We didn't build a dashboard. We built the answer, on a schedule, into an email. A fifth of the effort, and it got used — which the dashboard wouldn't have been.
Why it works: it answers a method question with a method, then proves it with one concrete case and a comparative outcome. Note that the example ends with something smaller than what was asked for — restraint reads as experience.