Frame "no" as "not now" or "here is what we can do instead" - always offer an alternative path forward.
Strong answers show courage with diplomacy: acknowledged the stakeholder's perspective, explained the reasoning with data, offered alternatives, and maintained the relationship. Look for evidence that they protected the team and product integrity without being confrontational.
Tests backbone and political skill. PMs who cannot say no build bloated products. PMs who say no without tact burn bridges. Look for the balance.