How do you diagnose a business right after acquisition?

Curious how operators here approach the first###-###-#### days after taking over a business. When you close, how do you quickly identify what's actually broken vs. what the seller told you? Do you have a framework, or is it mostly gut feel and conversations with staff? Asking because I've been building a diagnostic tool aimed at exactly this problem. not trying to pitch, genuinely want to understand how experienced operators think about it.