As many shoppers search for bargains in advance of Amazon’s “Prime Day” sale this week, there is a growing scepticism about how they can judge the products they are thinking of buying.

Three-quarters of people read the reviews posted about products and services, but doubts are mounting over the trustworthiness of these reviews. A burgeoning market for fakes has emerged, and experts say consumers must be vigilant.

So how can consumers know that what they are buying is reliable?

The rise of the fakes

Customer reviews have a huge influence over consumer spending, which is worth billions of pounds each year. When reviews are real, constructive and well-intentioned, they are of huge benefit to shoppers. Not so when they are fake.

A fake review will appear to have been written by a genuine customer but, unlike real reviews, they are paid for by the manufacturer or trader to boost ratings and rankings on sellers’ websites – which in turn boosts sales. In some cases companies give away goods or refund purchases in return for glowing reviews. But these practices are illegal under consumer protection law.

The Competition and Markets Authority (CMA) recently warned online giants Facebook and eBay about “troubling evidence of a thriving marketplace for fake online reviews” and urged swift action to remove the content.

The CMA’s investigations found businesses, agencies and individuals offering to buy or write fake reviews for cash on both online platforms, although the CMA did not believe Facebook and eBay were intentionally allowing this to happen.

Past work by the CMA has led to action. Online marketing firm Total SEO & Marketing was forced in 2016 to remove about 800 fake reviews it had produced for small businesses.

The CMA also made accommodation website Airbnb change its policy on customer reviews in 2017. Prior to this, if a customer arrived at a property but decided not to stay, or left early, they would not be able to automatically post a review online.

Consumer lobby group Which? has done extensive research on fake reviews and believes they are a growing menace. While Facebook and eBay have taken action after notification by the CMA, Which? says this is just the tip of the iceberg. “This is a massive and widespread problem online,” says the group’s Adam French.

Which? found tens of thousands of five-star “unverified” reviews on Amazon during their latest investigation in April this year. An unverified review is one posted by someone who did not purchase the item. Thousands of unverified reviews were posted on the same day and for the same products - typically tech devices, such as headphones, dash cams, fitness trackers and phone chargers with unknown brand names.

“There is a serious trust issue here and it discredits the selling platforms where the reviews appear,” says French. “The heaviest detriment falls on those consumers who can least afford it. Those people looking for a bargain, who cannot afford the big-name brands, stand to lose out.”

Why are they allowed?

Amazon says it invests significant resources into protecting the integrity of its reviews, using teams of investigators and technology to detect and prevent inauthentic posts. It says it has clear rules for reviewers and sellers, and will “suspend, ban and take legal action on those who violate policies”.

One of the best known consumer review websites – Trustpilot – also invests heavily to keep fakes at bay, with fraud detection robots and a 50-strong team. Trustpilot was criticised earlier this year for allowing companies to manipulate its systems by challenging genuine reviews that are negative or critical. Once a challenge is made the negative review is removed, but if it is later confirmed as “real” and reinstated it appears much further down the list of reviews and so has less prominence – a victory for the company. Trustpilot has agreed this is unfair and now publishes business-specific information about how often reviews are flagged for investigation. This way consumers can see which companies try to play the system.

Under consumer law, traders must “exercise professional diligence” towards customers: this means, for example, they must not make false claims about a product or service, or falsely represent themselves as a happy customer – for example by posting a positive review on their own website.

The British Standards Institute, which produces voluntary codes of conduct for different industries, has guidelines for online reviews, which say, among other things, that sellers should verify that reviews come from genuine customers, make sure reviews reflect the balance of all comments received (so not deleting negative reviews) and give users the opportunity to flag fake reviews.

Be aware

Martyn James from the online complaints service Resolver, which sees many disputes about online shopping, says that despite the law and voluntary codes, consumers need to be vigilant. He says those trading and creating fake reviews will always be one step ahead.

“It is a sad fact, but we all need to take a cynical approach to online reviews for as long as loopholes are found and exploited – which is likely to be for the foreseeable future,” he says.

But how can you tell if a review is fake?

• Be suspicious if a product has received a lot of five-star reviews in short space of time – on the same day for example. Be particularly wary if the product does not have a well-known brand. If the best-reviewed products are new or unheard of brands, and the top brands are ranked lower, be sceptical.

• Don’t just look at the star ratings of a product: read the reviews. Do they sound natural or are they short and repetitive, using a lot of the same phrases? If so, beware.

• Where possible, filter your search for verified reviews (this means the reviewer bought the item or service). But remember to also treat this with caution – sometimes a consumer may have been refunded for a product they bought in return for a positive review.

• Look at the reviewer’s history – have they given everything a five-star rating? What else did they buy? If they have bought 20 sets of similar headphones in the past week, for example, this should ring alarm bells.

• For hotel reviews, be wary of those that list the local amenities or attractions. Genuine hotel guests tend to focus on the room – space and cleanliness, for example, and hotel food: not what activities families can do nearby.

Facebook Twitter Pinterest Gareth Davies was hoping to buy a lawnmower. Photograph: H/O

‘It was a bit of an eye-opener’

Looking to buy a second hand petrol lawnmower, nurse Gareth Davies thought he had found just what he wanted: a Honda model, being sold by a private seller, and the product and seller had positive reviews.

“[Reviews are] a good way to gauge who you are dealing with and what you are buying. The reviews swung the purchase. I never suspected they were not genuine,” says Davies, from Washington, Tyne and Wear.

It was only when eBay got in touch to refund his money that he realised the problem. “It would seem the whole thing was fraudulent and there was no lawnmower. The product, seller and all the reviews had been made up. It was a bit of an eye-opener.”