Image copyright Iain Taylor

"I've learned never to rely on reviews for anything," says Iain Taylor, from East Sussex.

In his spare time and to supplement his income, the 44-year-old writes fake online reviews in exchange for money and free products.

"I have written reviews from numbing creams to eBooks to downloadable independent films," he says.

"I think it's bad - but I think everyone's doing it," says Mr Taylor, describing himself as "cynical".

"Since I started doing it I tell my family and friends not to trust reviews.

"If you are going to buy something you should do more research than look at a couple of five-star reviews on Amazon."

He says writers are paid to buy the product and then leave a review, meaning the review can be verified.

'Too focused on statistics'

Another person, a woman who preferred to remain anonymous, writes fake online reviews of the restaurant where she works - a chain pub in Nottingham.

"I feel like there's significant pressure to get positive reviews on either Facebook, Google or TripAdvisor," she says.

"The manager has actually told us to ask customers to do the review in front of us after their meals which I find hilarious.

"Anyway, I feel like it gets the managers off my back about it if I write a few for myself here and there. I do get a few genuine ones but a few more won't hurt, eh?"

She adds: "I think it does make me look like a better employee, obviously.

"That said, even if my manager knew I was doing it he would most likely encourage it because the company is far too focused upon statistics and increasing profit than actual customer satisfaction."

The murky world of fake online reviews hit headlines again on Tuesday, after consumer group Which? claimed that Amazon's website is flooded with fake five-star reviews for products from unfamiliar brands.

Amazon said it was using automated technology to weed out false reviews and that it had invested "significant resources" to protect its review system "because we know customers value the insights and experiences shared by fellow shoppers".

"Even one inauthentic review is one too many," it added.

Online reviews are valuable to businesses. The government's Competition and Markets Authority has estimated that such reviews potentially influence a mammoth £23bn of UK customer spending every year.

'You can't win'

One company, in Bingley, West Yorkshire has decided not to use review websites such as TrustPilot or Feefo because of the risk of competing with fake reviews.

Helena Gerwitz, head of marketing at Feature Radiators, says: "We work in a really niche industry.

"When new websites pop up, they might suddenly have 200 or so reviews. That's a lot of reviews since we know they have only been going since last month."

She believes the volume of the high-rated reviews that some competitors have cannot be legitimate.

Ms Gerwitz adds: "We have had chats about it - do we need to go down this route? - but my boss is very much 'we don't want to do that'. It's unethical, it's not true.

"We could set up a review account and know that we would do it legitimately but it would look bad as we wouldn't pay people to put out reviews, so relative to the other sites we would look terrible.

"So we have decided not to do them but then people think there is something to hide. You can't win. It's really frustrating."

'Lose faith in online shopping'

Even verified reviews might not be all they seem. Some consumers fear their personal data might have been used by sellers to gather fake "verified reviews".

Known as "brushing" the scam sees sellers obtain people's name and address to send the goods which they did not purchase.

On Amazon, this leaves a paper trail showing the goods had been bought on the site and had been delivered.

The seller then uses the individual's details to set up a new account which it uses to post glowing reviews of its products.

Amazon says it is "investigating" complaints of "unsolicited packages" which would breach the company's policy.

Architect Paul Bailey, from Billericay, in Essex believes he may have been targeted. Last month he received a number of unexpected "gifts", including a key-ring, a phone case, a tattoo removal kit and a charcoal toothpaste set.

"I think when the first parcel arrived it was a case of bemusement, then I checked with my wife if she'd used my account to buy something.

"When the second item arrived later that day I thought it was perplexing but amusing. Then it became quite chilling."

Mr Bailey says he cannot be sure where online sellers have obtained his data but says it has "made me lose faith in online shopping."

He added: "We all know there are laws in place over how data is handled but it's made me very, very nervous to the point I'm going shopping back on the High Street - even though it tends to be more expensive."

A spokesman for Amazon added: "We have confirmed the sellers involved did not receive names or shipping addresses from Amazon.

"We remove sellers in violation of our policies, withhold payments, and work with law enforcement to take appropriate action."

The psychology of online reviews

Nathalie Nahai, the author of Webs of Influence: The Psychology of Online Persuasion, says online reviews work because people try to take an "effortless route" when they have to make decisions.

"When it comes to purchasing, especially for items which are easy to buy, we expect this level of convenience and ease," she says.

"Part of that expectation is met by peer reviews… we can outsource our decision-making."

"Above a certain threshold, people will go for a slightly lower rating," Ms Nahai explains, citing a study where a product with more reviews but a 4.3 rating was more popular than the same product with fewer reviews and a 4.4.

Interestingly, she says there is "a certain leniency we give to bad reviews".

"We tend to distrust perfect ratings because it looks too good to be true," she says. "A five-star rating is less worthy than a 4.8 or 4.7."

It could also be the order of the reviews that matters.

Consumer psychologist Cathrine Jansson says some sellers might be aware of what is known as the primacy and recency effects. These theories state that people tend to remember the first and last items in a series better than those in the middle.

"It's the first five or six reviews that people tend to read and then if they're really interested they'll scroll to the last one.

"So some sellers will make sure it's really good reviews at the top and that people see a really good one last."

Nisa Bayindir, a director of market research company Global Web Index, says "consumers are getting more savvy" at spotting fake reviews and the most successful brands "focus on providing a good service".

She says the practice of fake reviews could be around for a while for cheaper products.

"Affordability can influence how much people research about a product. Sometimes people are just happy to pay a smaller amount of money for a mediocre experience."