The closest we can come to answering this question for you is yes, Marathon is shopped.
But we can't tell you who as we would be in trouble.
Go to the official list of mystery shopping companies and sign up for as many as you can and you will find it.
It does come up as an option for new shoppers so it isn't like you have to do any shops for it to show up (some MSC's only show certain shops for new shoppers).
Shopping across Indiana but mostly around Indianapolis.