A big scandal's kicked off in the world of books: big-name authors RJ Ellory and Stephen Leather have been writing fake reviews on the internet, bigging up their own titles and damning their rivals' books.
They're not the only ones - John Locke appears to have forgotten to mention "paying for hundreds of fake reviews" in his "how I sold lots of ebooks" guide - and if you think it only happens with books I've got a bridge I'd like to sell you.
Online reviews are utterly broken.
Take apps. If you've ever installed an app based on tons of five-star reviews only to discover a barely functioning game that constantly demands you pay £4.99 for some magic dangleberries, you'll know that there's often a big difference between what the reviews say and what the app's actually like.
I'm sure in some cases the reviewers are on the level - there are a lot of idiots out there - but I'm equally sure that fake reviews are rife. Apple may demand you buy an app before you can rate it, but that's no obstacle in the case of free ones - and with paid-for apps, you don't have to spend an enormous amount of money to get a decent number of reviews.
If those reviews shift a few dozen apps you've got your money back, and if that rockets you to the top of a particular category or makes you much more visible in the "people also bought" section then it's money well spent.
Whether it's a book, an app, a local restaurant or a plumber, if it can be give a rating or review online then sooner or later somebody's going to try and game the system. It isn't ethical, but it's effective: if it wasn't, fake-review operations wouldn't be generating tens of thousands of pounds every month.
It happens because it works
You can see the appeal. Imagine you have a restaurant, and in these tough times you need every customer you can get - so why not try to steal your rivals' customers? Why not pay a few friends to go to your rival's restaurant, booking via one of the restaurant booking sites, and then leave a damning online review for other would-be diners?
It wouldn't cost much, and if it persuades even a couple of people to go to your restaurant rather than theirs then it's been a good investment.
I bet it happens in consumer electronics too. A story doing the rounds today claims that Samsung paid for bloggers' flights and accommodation to IFA 2012, then threatened to leave them stranded when they refused to be PR puppets; Samsung's anger at the refusal strongly suggests that they've done it before and the writers acquiesced.
Reviews often have an agenda, but unfortunately you can't always tell by looking at them. Is that laptop great, or does the reviewer work for a reseller? Is that book really bad, or is a rival author trying to poison it?
Not all reviews are worthless, of course, but they can be hard to find. I've some experience of this: as a self-published author on Amazon I've received really measured, thoughtful, critical and interesting reviews but also reviews suggesting that my book is better than toast (it probably isn't) or that it's worse than Hitler (I'm pretty sure it isn't that either).
I've also seen a discussion on Twitter between two people planning to leave a really bad review because they didn't like me at school 27 years ago.
Do you really want yahoos like that to guide your buying decisions?
Most online reviews are noise, and the trick is to ignore it and find the reviewers you can trust. They could be specific reviewers on Amazon, or on Goodreads; they could be reliable sources of app reviews such as Tap!; they could be particular people on this very site. Good reviewers are worth their weight in gold; biased ones aren't even worth reading.
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Writer, broadcaster, musician and kitchen gadget obsessive Carrie Marshall (Twitter) has been writing about tech since 1998, contributing sage advice and odd opinions to all kinds of magazines and websites as well as writing more than a dozen books. Her memoir, Carrie Kills A Man, is on sale now. She is the singer in Glaswegian rock band HAVR.