> How will you know it's a comprehensive exposé?

How about before I purchase there's an excerpt and the number of words that lay ahead? I mean, it couldn't be that hard to distinguish comprehensive articles vs the norm.

> How will you evaluate whether an article is going to be worth the price?

I wouldn't know. And if it wasn't worth it, I probably wouldn't purchase a future piece from the same reporter. That said, there could be a review system. (Just brainstorming here)