What proof point makes a SaaS pricing tier easier to trust?

A pricing-page question about explaining plan boundaries with workflow evidence instead of only feature grids.

When a pricing page has Starter, Pro, and Business tiers, what proof point helps the buyer most: usage volume, time saved, support speed, audit history, team seats, or an example of the workflow limit? Feature grids are useful, but I usually need one sentence that says when the plan becomes the right choice.