My observation of other artists ratings is that statistically more negative rating are on the cheaper products. So probably amateurs which are preferreing lower prices are more probable to give negative rating than same professional which buys expensive (or adequatelly priced) product - yes if the expensive product is trully bad then professional can give also negative rating - but in most cases it is from amateurs I think so in other words I agree with you.
Probably the only solution is to more concentrate or compex and expensive products. ))))