Bookstore owners everywhere have a lurking suspicion: that the customers who type into their smartphones while browsing in the store, and then leave, are planning to buy the books online later — probably at a steep discount from the bookstores’ archrival, Amazon.com.

Hiroko Masuike for The New York Times

Now a survey has confirmed that the practice, known among booksellers as showrooming, is not a figment of their imaginations. According to the survey, conducted in October by the Codex Group, a book market research and consulting company, 24 percent of people who said they had bought books from an online retailer in the last month also said they had seen the book in a brick-and-mortar bookstore first.

Thirty-nine percent of people who bought books from Amazon in the same period said they had looked at the book in a bookstore before buying it from Amazon, the survey said.

As frustrated bookstore owners see it, the practice allows customers to take advantage of the stores’ careful selection of books, staff recommendations and warm atmosphere — all while spending their money elsewhere.

Valerie Koehler, the owner of Blue Willow Bookshop in Houston, said she had occasionally spotted customers who appeared to be typing titles into their phones instead of buying the books.

But she also suspects that the small size of her store helps her in this regard, because it has an intimacy that discourages offenders, she said.

“There’s really not much anonymity here,” Ms. Koehler said. “I think most people are coming in because they want to get something here.”

But Peter Hildick-Smith, the president of the Codex Group, said publishers and bookstore owners should be worried about the practice, especially considering the rapidly increasing number of e-readers in circulation.

“It is a real concern,” Mr. Hildick-Smith said. “The two forces combined are going to put even more pressure on bookstore sales in the new year, unless publishers can do more to support the book retailer just as movie studios have historically done to support the movie theater.”