Originally Posted by
lcpteck
So how does one know the fare code equivalent on the operating carrier? Talk to the marketing carrier?
I guess maybe I should buy the ticket from the same airline that is operating the flight to avoid all this hassle.

I'm not sure I understand the question. In your example, are you seeking to credit miles to United or ANA?
If United, their policy is "The award miles accrued on codeshare flights are based on the operating carrier and their equivalent fare class."
United has categories of classes (first, business, full fare economy, economy, and discount economy) listed for ANA. Try and match that term, not the letter.