Yes and no. You have a point, but I don't think you need every bidder to have this oracle. If only one bidder could tell the difference, that bidder might just

Yes and no. You have a point, but I don't think you need every bidder to have this oracle. If only one bidder could tell the difference, that bidder might just buy fewer ads because ROI estimates will be lower, so fewer ad buys would look like positive ROI. Of course, that's under the assumption that fraud inflates performance metrics, but I think that's a pretty safe assumption.