This is incredibly open to abuse by both vendors and their competitors. A rater's "realness" is probably much better judged by other measures of marketplace act

This is incredibly open to abuse by both vendors and their competitors. A rater's "realness" is probably much better judged by other measures of marketplace activity or simply equal weighting than by their willingness to pay to bias the ranking of a particular review. I'd tend to defer to what's worked in other (semi) anonymous markets -- it's pretty easy to tell when someone is real or not based on their activity patterns. A better policy is probably to keep raw information available and let people parse it in different ways, rather than baking in a risky and probably fragile system we hope will work.