At Newegg they have reviews by \"verified owners\" in addition to unverified owners. I find it helpful when parsing the reviews.
Fraud typically requires the following four elements.
* an individual or an organization intentionally makes an untrue representation about an important fact or event:
* the untrue representation is believed by the victim (the person or organization to whom the representation has been made);
* the victim relies upon and acts upon the untrue representation;
* the victim suffers loss of money and/or property as a result of relying upon and acting upon the untrue representation.
I fail to see how pretending to be somebody else would absolve anyone on liability. If instead of on-line reviews a salesman suggested a person call some phony customers or presented phony testimonials, we would have no issues calling it fraud. So why would it not be fraud to write fake testimonials where something is going to be sold?
While these reviews are opinions, the untrue element is that the reader will believe these multiple reviews are coming from independent sources who are most likely owners of the product or who have at least seen it. While that may not be explicit, it is certainly implicit. Is that an important fact? That is debatable. I know that on Newegg that I am far more likely to purchase something that has lots of reviews if those reviews tend to be positive and do not indicate any major compatibility issues (Newegg sells a lot of computer components). I do not like being the first to buy something.
My guess is that it is simply not worth the effort to prosecute cases of bogus reviews, especially if the sales cross state lines. It would take a lot of effort to prove who actually posted the reviews, and that involves obtaining IP addresses and subsequently identities tied to IP addresses. It would be trivial to use proxies to make these reviews, and my guess is that one of the easiest safeguards Amazon (or anyone else could take) would be to flag multiple accounts from the same IP address in a relatively short period of time, which would mean proxies were likely used.
Fraud laws tend to be vague enough to cover new techniques for fraud while being specific enough that one should know if it is illegal or not. I think this technique qualifies, but I am not a lawyer - I just throw rotting vegetables at them.