In the world of online shopping, often buyers will purchase an item only after they see that other people also like it. And the easiest way to find out consumer sentiment? You guessed it: reviews.

But should you trust customer reviews when deciding what to purchase? And do these mysterious reviewers have your best interests in mind?

Consumers today are skeptical, said Zach Pardes, of the review platform Trustpilot. Shoppers use Trustpilot to read about companies and write reviews, while businesses use it to collect reviews.

"We live in a time when trust is completely under attack," Pardes says.

It seems shoppers are skeptical for good reason. Fake reviews do exist, according to Saoud Khalifah, CEO of Fakespot, a platform that analyzes online reviews. Fake reviews include, but aren't limited to, bot-generated reviews and reviews that are influenced by the seller.

So why are fake reviews out there? Khalifah said consumers are wary of products with no reviews or zero stars. A number of positive reviews can make a product look better.

Of course, not all user reviews you read online are fake. Authentic reviews are a valuable tool when making a variety of purchases. They can help consumers make important financial decisions by learning about someone else's experience. This may include which hotel to book, where to eat dinner or what brand of vacuum to purchase.

Pardes says Trustpilot features flagging mechanisms visible to users, plus artificial intelligence technology and a team in place to detect and remove fake reviews.

Perhaps one of the best-known review websites is Yelp. Kathleen Liu, a company spokeswoman, compares the popular site to a modern-day version of word-of-mouth.

Yelp takes measures to ensure "high-quality content," Liu says. That includes allowing Yelp's community of business owners and users to flag content that may violate the site's terms of service, as well as human moderation of reviews.

Since legitimate user reviews do provide helpful information, reviews as a whole shouldn't be discounted. But how can you tell the difference between what's real and what's not? It's close to impossible for the everyday consumer.

But if you do your due diligence, you can make an informed purchase.

• Check more than one review source. Pardes advises consumers to read reviews on multiple platforms. "If you're about to book a $10,000 vacation, you'd never rely solely on the photos and the reviews posted by that hotel's marketing team," he says. "You're going to want to use a third-party independent resource."

• Read more than a handful of reviews. Pardes said there is "safety in numbers."

• Watch for warning signs. For example, does the review focus more on the company and its customer support than on the actual product? This could indicate a reviewer was influenced by the seller or company, Khalifah said.

• Question perfection. Pardes said consumers don't trust reviews that show only five stars. "Nobody's perfect, so you can't possibly have a perfect five-star review in every single category of your business," he said.

Courtney Jespersen is a writer at NerdWallet. E-mail: courtney@nerdwallet.com. Twitter: @CourtneyNerd.