Frequent four-grams included “in the middle of,” “the rest of the” and “at the end of.” That fits with Dr. Vásquez’s observation that when people write about hotels, recipes or diaper bags, they like to tell stories. Narratives, she found, are more likely to appear in negative reviews than in positive ones.

Dr. Vásquez isn’t the only linguist taking a look at online reviews. In April, the computational linguist Dan Jurafsky at Stanford and others from Carnegie Mellon published an analysis of nearly 900,000 Yelp reviews of more than 6,000 restaurants. They found that reviews of more expensive restaurants generally contained longer sentences, suggesting a link between income and education levels. Also, the linguists suggested that writing a bad review was a way to cope psychologically with a negative experience.

Many people who shop online encounter all sorts of online reviews without giving them much thought, except in one regard: their veracity. Dr. Vásquez says she is often asked about fake reviews. A typical red flag is that they are usually posted by someone who has no other reviews listed and they don’t describe the product or service with certain details.

In 2011, researchers at Cornell University discovered that fake reviews tended to use more superlatives than real ones and used “I” and “we” more often. Companies use algorithms, presumably built on these linguistic principles, to remove fake reviews. But there may be more telling indicators. Dr. Vásquez says that one possible sign of a fake hotel review is an absence of spatial information about the room.

Then there are the reviews that a company asks customers to write, like the type Dr. Vásquez encountered at the car dealership. They are not outright fraudulent, nor are they to be viewed completely without suspicion. Solicited reviews occupy a kind of gray area, and she says it is hard to know how many are out there, as most reviewers don’t disclose whether their comments were solicited.

Despite a popular focus on fraudulent reviews, Dr. Vásquez says they are a small fraction of all reviews, so she focused her efforts on the elaborate storytelling and displays of expertise in reviews on the five sites she studied.

As Youngme Moon, a professor at Harvard Business School, noted in her book “Different: Escaping the Competitive Herd,” consumers come to know a lot about certain categories of goods and services. A review is a demonstration of their knowledge. And on some sites, consumers’ reviews can look a lot like lifestyle mini-blogs. (Hey, look at me, I shop at Patagonia, and I demand a lot from my shoes.)