you might also find my earlier comment relevant - http://news.ycombinator.com/item?id=3972595

I think that fake reviews (shilling) is a special class of problem. I don't believe it fits any of the normal categories of fraud (i.e. that's why I was happy it kind of was artificially added there) and yet I believe that what we lose by not regulating it is an important enough commons that it should be protected.