The reviewers may not be qualified
They review their latest car/camera/washing machine but they have no experience of a comparable product. Their review is made up of a combination of the 'honeymoon effect' (the instinctive positive feeling for a new purchase) and self-regard (no-one wants to look foolish for buying a lemon).
Just look at the disparity between the experts' verdict and the purchasers' for this car:
We're pretty sure that had product reviews been around when Ladas were on the market, their loyal owners would have rated them pretty highly as well!
Products often need time to prove themselves
This means that the value of a review garnered immediately post-purchase has a much reduced value for the prospective customer.
|5 Stars for looks? 5 stars for delivery? Maybe it would be more helpful to ask for the review a year after purchase?|
Reviewers rate aspects of the purchase that are not related to the product
|Helpful - in isolation - but not when the score is taken into account to rate the product|
Often the website, the ordering process and especially the delivery service. Whilst all important aspects of the overall experience, they should not be (but are) confused with reviews of the product.
Of course, in the short term, a great rating benefits the business (we know great reviews drive business, after all), but in the long term customers will become wary of product reviews if they don't give them what they want, and we don't see how they can.
Service, on the other hand, is always either 'good, 'bad' or 'indifferent'. You don't need to be an expert in hotels to have an opinion on their level of service, you don't have to use multiple accountants or estate agents to have a pretty accurate take on their professionalism.