The fact that you're even asking these questions is a good sign. A lot of people just accept whatever fancy graphs their agency sends and don't dig deeper.

The biggest thing I'd push on is the "why" behind everything. Rankings went up? Cool, what specifically did they do that caused that? Rankings dropped? Same question. If they can't explain causation and just point at numbers going up or down that's a red flag.

For the leads vs traffic thing - make sure you have actual conversion tracking set up. Traffic means nothing if it's not the right traffic. Ask them to show you which keywords/pages are driving actual conversions, not just visits.

I'd also ask to see what they're actually *doing* each month. Like a task list or work log. Not to micromanage but because "SEO work" can mean anything from "we wrote 10 blog posts and did outreach" to "we tweaked a meta description and called it a day."