Really? That means you basically want to know what profit margins they’re running at… which no business would want to (or should need to) reveal

That's exactly what's happening to you when you're the prospective buyer in one of those calls.

I'm not in sales, but I've had a job once where I could see all the financials. And we would very often be charging one customer 10x what we charged another for exactly the same tier of service. Sometimes the huge corps would be paying more for a lower service tier than a small corp on a higher tier.

You can find that information in quarterly published information for all publicly traded companies, and for many non-public companies with only slightly more searching.