"The problem is that comScore (and now Yelp) have an economic incentive to get people to advertise such that they are not impartial and site therefore cannot be

"The problem is that comScore (and now Yelp) have an economic incentive to get people to advertise such that they are not impartial and site therefore cannot be trusted." That's a key part of it. They do two things: keep track of a "fair score," and sell to some of the businesses being scored. It's an inherent conflict of interest. And they have not taken any steps to mitigate it. Google faces the same problem, but the AdWords auction mechanism diffuses the COI so the temptation to extortion is mitigated. As some have pointed out farther down, newspapers and magazines have the same problem. Serious newspapers have a wall between editorial and advertising to mitigate the COI.