Does this sound familiar?

You’ve read rave online reviews about a restaurant or hotel and made a reservation. Then you show up and wonder if you’re even in the same place the reviewers visited.

That’s when you know: They were fake reviews.

Phony reviews make up a big percentage of the total out there—anywhere from 16% to 40%, according to some estimates. Some fakes are raves by employees, artificial-intelligence software or people hired to wax poetic about the place. Others are negative write-ups by disgruntled ex-employees or competitors.

The problem is so widespread that the Federal Trade Commission just created a new rule that will seek civil penalties for violators who pay for fake reviews or testimonials. Meanwhile, review platforms and online travel agencies are stepping up their efforts to weed out fake reviews before they ever show up online.

It isn’t easy for people to distinguish real from phony. Shabnam Azimi, an associate professor of marketing at Loyola University of Chicago, conducted research that aimed to determine whether humans are good at weeding out fakes. “We found that overall, humans detect real reviews about half of the time,” says Azimi. “We are no better at lie detection than chance.”

The good news is that researchers and seasoned travelers have found a number of effective strategies for spotting fakes. Here are some of their best tips.

Look for a picture

One distinguishing mark of dubious reviews: no profile photos.

Lawrence Hoc Nang Fong, an associate professor in tourism management at the University of Macau, studied reviews that Yelp designates as “not recommended” because, he says, they set off alarm bells as potential fakes. (A Yelp spokesperson says that these reviews are not necessarily fake, but that Yelp’s software determines them to be “less reliable and useful.”)

In the study , “46.9% of the fake reviews do not have profile pictures of the reviewers, while 19.9% of the authentic reviews do not have profile pictures,” he says. “So look for profile pictures to help determine which reviews are real and which are not.” Readers can also do an online image search on profile pictures to see if the person is really who the profile claims to be.

‘We’ can be a warning sign

Swindlers who are hired to write fakes don’t like to use the word “I.” In a paper published last year , researchers found that fake-review writers avoided the use of first-person-singular pronouns and go for “we” instead. Why? Some of the fake reviewers who were recruited for the study said they used collective pronouns to share accountability with imaginary others (like a pretend family) and to create some psychological space between them and the presumed reader. Of course, the use of “I” instead of “we” won’t always reveal a fake, but it can help in your decision process.

Check the timing

When reviews are posted can be another important clue. Clusters of similar postings popping up around the same time might reveal a solicitation campaign, according to recent research . For instance, companies might purchase a bulk of fake reviews from gig-worker sites or turn to AI writing assistants just before a major event, like a big marathon, when they know travelers are on the hunt for reservations.

Alton Chua, an associate professor at Nanyang Technological University in Singapore, suggests reading the reviews preceding and succeeding any single post. “For example, if several similar reviews are posted with largely similar texts and in proximal time intervals, alarm bells should go off,” the researcher says. Likewise, “similar images used across reviews are also a telltale sign of inauthenticity.”

Details matter

Fraudulent reviews are often light on details but are packed with exclamation marks, all-caps words and vague superlatives such as “awesome” and “awful,” according to research. Fake reviews also tend to be shorter than real ones: The research suggests that authentic reviews contain fewer long words, but longer sentences. Paid reviews, meanwhile, tend to be short in both words and specifics, since fake-review-farm writers are typically compensated for the number of postings, not necessarily their length, according to experts.

Real reviews, on the other hand, often have specifics, such as anecdotes about a trip or details about the meals people were served.

“If the review says, ‘It’s so pretty,’ and the wording seems staccato, I don’t buy it,” says Meg Nolan, a travel adviser with Friend of a Friend Trip Design, based in West Palm Beach, Fla. “On the other hand, if someone writes six sentences about how the check-in staff gave them a spare room to change in so they could use the pool while they waited for their room to be ready, that level of details leads me to assume it’s written by a real guest.”

Particularly important, according to research out of Cornell University, is the use of spatial configurations, such as how big a guest room is or which direction the balcony faces—details that reviewers would likely not know unless they had stayed at a property. Similarly, the study concluded that the use of a lot of concrete and sensorial language—words associated with hearing, touching, tasting, smelling or seeing—is a decent proxy for honest reviews.

However, experts suggest that one specific concrete detail may be a warning sign: using an employee’s name. “It’s possible the hotel or restaurant offered some sort of prize for the person who got the most reviews that week,” Nolan says, so the worker may have asked people to write fake notices. “Ignore them,” Nolan says.

If you’re worried about AI-generated reviews, studies done internally by big travel-review sites have shown that AI software is pretty bad at spatial indicators and often lacks that human spark known as personality. But be warned: AI will get better.

Do some cross-checking

Another way to protect against fake reviews is to look across several sites for write-ups of the same hotel, restaurant or tour operator. Check to see if reviews have been simply copy-and-pasted from one site to the other (“I assume that’s fake,” says Nolan), and if they are consistent. At the very least, reviews across platforms shouldn’t be trusted if they can’t even get basic facts right, like whether a property has a pool or is bombarded with street noise.

Avoid the extremes

When they are perusing reviews, seasoned travelers like Rahul Mehta, a finance executive and frequent traveler, often strip out one- and five-star write-ups. Typically, heavy travelers like Mehta say that five stars simply communicate that the place or experience delivered exactly as expected, which is “the bare minimum, and not really meaningful information,” while one star could be an outlier or someone who has a beef with the front desk. At worst, they are fake; at best, they aren’t very useful.

Mehta says he puts more stock in the middling reviews than the extremes. “A property that has two five-star reviews carries less weight than another property that is rated four stars by 85 reviewers,” he says. He will set a filter to isolate the two- to four-star reviews, then will read a handful of the negative ones. “The positive ones repeat the same stuff,” he says. “What’s new information for me are the negative reviews.”

Heidi Mitchell is a writer in Chicago and London. She can be reached at reports@wsj.com .