If the marketer is an employee or a consultant, is it in their interest to show that the ad-spend they are controlling is high ROI, or low ROI.

Maybe this is a cynical take, but, if they get to the bottom of things, and show their boss/client that the ad-spend is not returning so much, it seems it would portend bad things for the marketer.

I really don't know, and it seems like a very hard problem.

Maybe this is the time for that Upton Sinclair quote: "It is difficult to get a man to understand something, when his salary depends upon his not understanding it,"