• The bot armies. Sleazy sellers can buy blocks of fake Amazon customer accounts by the thousand. Then they use people or software bots to write fake five-star reviews for their own products. (They’re careful to make subtle changes to each review — varying the number of exclamation points, for example — so that Amazon’s algorithms won’t spot the duplicates.)

• The bait-and-switch. Once a seller has earned a high rating for a product, he can swap in a different photo and description, and voila: Instant high ratings for a completely unrelated product. Check out the page for this flash drive, for example, where (at this writing, anyway), the various reviews refer to a paper calendar, a blanket, a tooth-pain medicine, and binoculars. This seller has switched its product on this page, in other words, multiple times.

• The praise-your-enemies trick. Sometimes, sellers leave crude, obviously phony five-star reviews for competitors’ products. These reviews are engineered to trigger Amazon’s own algorithms, so that their competitors get suspended. (Alternatively, they click the “Helpful” button on negative reviews for rival products, so that those reviews rise to the top.)

Amazon, in an effort to foster growth, has been inviting more Chinese companies (and U.S. sellers selling Chinese goods) to list their wares on the company’s site. (Only about half of the items listed on Amazon are actually sold by Amazon. All the rest are shipped directly to you from “third-party sellers,” who may use Amazon packaging to make it feel more Amazon-ish.) As you can guess, that trend makes the fake-reviews problem even worse.

How to spot the fakes

All right. Now you know what you’re up against. But you have some tactics at your disposal, too. Here are a few ways to tell fake reviews from good ones:

• Check the reviewer’s profile. When you click a reviewer’s name (which appears above every review), you get to see her profile page, which is often extremely enlightening. It shows all of this person’s reviews, for all products, all clumped together. If it looks like they’re all on the same day (or couple of days), or if they’re all variations of the same comments, you should smell a rat.

• Check the wish list. “You don’t even need to look at the reviews,” says FakeSpot’s Khalifah. “Look at the wish list! Nobody ever looks at the wish list.” At the left side of a seller’s profile page, you can click one of his Wish Lists. If you see the same items over and over again, even though you’re inspecting different reviewers’ profiles, you’ve found a cheat.

• Look at the three- and four-star reviews. One aspect of a fake review you can count on: It’ll be a five-star review. (Or, when a seller is trying to attack a competitor, a one-star review.) A two-, three-, or four-star rating doesn’t accomplish much in moving a review’s search-results position. Therefore, the in-between ratings are more likely to be authentic — and therefore worth reading.

• Watch out for one-worders. The name of the game is the star rating; the higher the average rating, the higher the product appears in Amazon’s search results. Therefore, fake reviews are often very short and non-specific (“Great!!”), because the actual prose of the review doesn’t affect its attractiveness to Amazon’s search algorithms.

• Watch out for compensated reviews. Until October 2016, you were allowed to post a review you’d written in exchange for free stuff, as long as you revealed that you’d gotten a gift. It quickly became clear, though, that those reviewers were far more likely to leave positive reviews (shocker!) — and in October 2016, Amazon barred the practice. Those older reviews are still hanging around, though.

• Beware the Vine. Incredibly, Amazon itself encourages a similar sort of compensated review to this day, in the form of Amazon Vine. That’s a program that sends you free products in exchange for reviews. You have to be invited to become a Vine reviewer (based on your history of leaving well-regarded reviews), and sellers have no direct contact with you. Still, it seems rife with bias. Sellers pay Amazon for the reviews (from $2,000 to $7,500, according to Khalifah), and send the free products for Amazon to pass along to the Vine reviewers. As noted above, it’s human nature to give a higher rating to something you got for free. At least Vine reviews are clearly marked.

• Trust older reviews. The widespread gaming of Amazon reviews is a relatively recent phenomenon. “Any review before 2013, you could put a lot of trust in,” says Khalifah. (The exception, of course, is if you spot an old review that describes a completely different product. In that case, the seller has swapped in a different product.)

Let someone else do the work

Obviously, that list of traits that characterize good and bad reviews entails a lot of work on your part, especially if a product has hundreds of reviews. You’d be wise, therefore, to paste the page’s link into FakeSpot or ReviewMeta. These sites check out all of the reviews for the product at once.

“There are so many angles, so many variables,” says FakeSpot’s Khalifah. “We take a look at all the reviews for the product. Then we look at the all the reviewers themselves, all their historic reviews, all their wish lists, and try to find any patterns.”

FakeSpot shows you how many of the reviews it suspects are bogus, and clearly explains its reasoning. ReviewMeta actually recalculates the Amazon star rating for you, based only on the reviews it suspects to be valid.

Each site offers a web-browser extension (plug-in), so that you don’t even have to do the copy-and-paste thing. (FakeSpot’s extension is currently $2 a month, but Khalifah says that it will be free soon.)

What’s Amazon doing?

The fake-review problem is getting worse; Amazon says that it’s up for the challenge. “We know the value of reviews for customers, and even one inauthentic review is unacceptable,” the spokesperson told me. “Customers can report suspicious reviews 24 hours a day, 7 days a week, and we investigate each claim. We take forceful action against both reviewers and sellers by suppressing reviews that violate our guidelines, and [we] suspend, ban, or pursue legal action against these bad actors.”

The company bans sellers and fake-review accounts by the thousands; each time, it uses machine learning to improve and anticipate the sellers’ ever-evolving tactics. Amazon also works with Facebook to shut down those “free stuff for five-star review” groups, and has filed over a thousand lawsuits against sellers and fake reviewers.

Both Khalifah and Noonan say that they can see Amazon’s efforts at work. “My data does show that Amazon is deleting tons of reviews — literally millions of reviews,” says ReviewMeta’s Tommy Noonan.

But it’s an arms race, a cat-and-mouse game, and it’s not clear that the good guys are winning. Amazon and other review-based companies are increasingly fighting the same kinds of trust battles that are hobbling every aspect of the internet these days. It’s no longer enough to be a good judge of value and quality when you shop; now, you’re expected to be a good judge of the reviews that are supposed to guide you.

David Pogue, tech columnist for Yahoo Finance, welcomes comments below. On the Web, he’s davidpogue.com. On Twitter, he’s @pogue. On email, he’s poguester@yahoo.com. You can sign up to get his stuff by email, here.

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