Retaining trust is especially important as audiences have come to regard documentaries as a vehicle for long-form investigation, the kind that the news media may no longer do. The strength of the Netflix docu-series “Making a Murderer” (which Mr. Powers showed at Doc NYC) “is that those two filmmakers could take the 10 years” to delve into the case, Mr. Powers said. (Nonetheless, its reporting was also questioned.)  But David Wilson, a programmer and co-founder of the True/False Film Fest, a respected annual showcase in Missouri, said it was a mistake to routinely treat documentaries in the same way as journalism. “I think documentary films are often not the right way to lay out the complex case for and against something,” he said. “They can tell great stories, they can create empathy and capture the messiness of the human condition.” But, he continued, “in no way does documentary film stand next to an article in Science magazine or The Lancet,” the British medical journal.  Asked whether programmers should accept a film if they are not certain of its veracity, Mr. Wilson said, “My answer is an emphatic ‘sometimes.’” Drawing on the director Werner Herzog’s maxim that he is after the truth of poets, not the truth of accountants, Mr. Wilson added, “We show films that many people would look at and say, ‘How is that possibly a documentary?’”  Among its most recent selections was “Tickled,” a film that on its surface is about a subculture of tickling fetishists but probes further to discover possible threats and online bullying. “We were receiving legal threats even before we’d started production,” Dylan Reeve, a director of the film, wrote in an email, adding that they were concerned that this would hinder its acceptance by festivals.  Though most organizers say festivals do not have the resources or the mission to fully investigate everything, Mr. Powers does consider, for example, whether films have all the legal rights to their material. (Last year, Aretha Franklin won a court battle that resulted in the documentary “Amazing Grace,” which included vintage concert footage of her, being pulled from several festivals, including Toronto.)  “Tickled” premiered at the Sundance Film Festival. At its screening at True/False, its director David Farrier was served with legal papers charging defamation and related complaints. Mr. Wilson said that in programming it, he and his team “looked closely at the claims it made, and we felt those claims are honest.”  In some cases, curators call for backup. The 2009 film “Stolen,” which charged that there was modern-day slavery in West African refugee camps, ran into criticism after a screening at the Sydney Film Festival in Australia. So before he added it to the Toronto schedule, Mr. Powers contacted a human rights expert to confirm that its depictions were fair, he said. The film played at Toronto and in 2013, with extra reporting, ran on PBS. (Television networks, which can be considered liable for false claims, tend to do more thorough vetting.)  Eamonn Bowles, president of Magnolia Pictures, the distributor of “Tickled,” said the company did not rely on festival programmers for verification of its material. He wrote in an email that he was prepared to “encounter some unsavory tactics” from the film’s subjects during its rollout, but had faith in the filmmakers.  One way to clarify what is acceptable in documentaries, especially as technology has made it easier for anyone to make them, is to create standards or industrywide best practices. But that, too, is a divisive proposal. Mr. Wilson, of True/False, was “categorically not in favor,” he said, because he felt it would be stifling to filmmakers.  Professor Aufderheide, who has researched ethical quandaries among documentarians, found widespread concern that guidelines could be used against directors, especially in legal claims. “Lawyers will push the letter of the code — ‘You were not doing the best practice, and so we can sue you,’” she said.  “In a way it breaks my heart,” she added, “because people are hungry and thirsty to know that they are standing with the best standards in their film.” At documentary conferences, sessions on the topic are always packed, she said.  For their part, festival organizers say it is also up to audiences to sniff out what is legitimate and what is not. “I think we should be teaching media literacy in every high school in the country,” Mr. Wilson said. At True/False, “we encourage and push our audiences to be critical viewers; we want audiences to take on the task.”  And, Mr. Powers added, moviegoers need to be realistic about the limitations of cinema. “It’s kind of important to understand,” he said, “that one film is not the fulfillment of the search for truth.”  A version of this article appears in print on April 6, 2016, on page C1 of the New York edition with the headline: Film Festivals Feel Push on Truth. Order Reprints| Today's Paper|Subscribe
As the number of films grows, film festival programmers face more pressure to serve as judges of fairness and accuracy.