It’s probably better to own up at the start. I recently bought new sunglasses online. They arrived promptly and after waiting patiently for a sunny day in the north-east, they lived up to expectations.

A couple of days later, I was surprised by an email from the seller, promising another pair in return for an online review. An Aberdonian upbringing quickly outweighed the admittedly short-lived moral dilemma. After all, the glasses were competitively priced, had arrived quickly and seemed to do the trick.

As a result, I didn’t feel too bad about providing a five-star review. Sure enough, two weeks later the promised second pair popped through the letterbox. I don’t feel I did anything wrong, as my review wouldn’t have misled a prospective buyer.

Shortly afterwards, I received another email from the vendor asking if I would be willing to review more of their products: the incentive being I could keep the items. At that point moral scruples kicked in and I declined.

The experience did however, raise questions about online reviews. Who writes them and why do they do it? I don’t normally write reviews and wouldn’t have done so without the carrot of a freebie. Would I still have received it had I provided a two-or three-star review? To what extent are online buyers influenced by reviews like mine?

The last question is easily answered. Online reviews are hugely influential. Surveys by Which? suggest an astonishing 97% of prospective buyers pay heed to online reviews. That alone demonstrates their importance to vendors. It also explains why generating fake reviews is big business and why the Competition and Markets Authority (CMA) takes seriously paid-for, incentivised and fake reviews.

The CMA estimates that online reviews influence around £23billion of consumer spending. Investigations by the BBC and Which? suggest that 20 to 40 percent of online reviews are fake. Bot-generated fakes are fairly easy to spot, repeatedly using the same words, phrases and formats. Additionally, bots have a humour bypass. As a result, unscrupulous sellers use “review farms”, enlisting humans to write flattering or even misleading reviews.

In the gig economy, writing fake reviews supplements income. Technology makes it easy to “game” the system and write reviews of products and places that “users” have never purchased or visited. Investigation by the BBC revealed fake reviews written for as little as £4. One restaurant worker was expected to write fake reviews as part of her job. Possibly, the most outrageous example of gaming the system was perpetrated by journalist Oobah Butler and his pals who manipulated The Shed in Dulwich to the top of Trip Advisor’s London eateries. There was a slight drawback for influenced, would-be diners – the restaurant didn’t exist.

That’s not to say all reviews are fake or misleading. Psychologists have tried to explain why people write reviews. For some, it’s a genuine wish to help others and are undoubtedly useful. Others have less worthy motives. It could be a power and ego thing, having a voice and influence. People who review restaurants and hotels for example, are well aware they are read and taken seriously by owners and managers.

But there’s a huge difference between an honest critic and a troll who sets out to inflict reputational and economic damage. Psychologists tell us those who have had a negative experience are more likely to write reviews because negative emotions tend to be stronger and longer lasting.

Given the scale and power of fake reviews, it’s surprising it has taken the government so long to make it illegal for platforms to pay for or host fake reviews. Most reputable sites take fake reviews seriously and work hard to weed them out. Many employ human “spotters” as well as algorithms to root out fakes.

Nevertheless, some will slip through and then it’s a case of caveat emptor and we need to spot the suspect ourselves. Examining a reviewer’s profile can ring alarm bells. Which? for example, warns of “once only” reviewers although, as Trip Advisor points out, “every reviewer in the world is at some point a first-time reviewer”. A critical review reader will ignore the outliers, good and bad, and three and four-star ratings may be more reliable. If a full house of five-star ratings seems too good to be true, it probably is.

Our columns are a platform for writers to express their opinions. They do not necessarily represent the views of The Herald.