> And it doesn't freak you out that you're relying on thousands of lines of code that you've never looked at?

I was a product manager for 15 years. I helped sell products to customers who paid thousands or millions of dollars for them. I never looked at the code. Customers never looked at the code. The overwhelming majority of people in the world are constantly relying on code they've never looked at. It's mostly fine.

> How do you verify the end result?

That's the better question, and the answer is a few things. First, when it makes changes to my ad accounts, I spot check them in the UI. Second, I look at ad reporting pretty often, since it's a core part of running my business. If there were suddenly some enormous spike in spend, it wouldn't take me long to catch it.