This goes double if said story is of the "supernatural" purporting to be true. The truth is likely to be cherrypicked at best but more likely steamrolled over if not tossed aside completely. People always have an angle and when it comes to claims for which there is little or no evidence, even more scepticism than usual is warranted. Films always fictionalise by their nature, but how much truth is at the heart of a story? The more supernatural the claim, the more scepticism should be applied.

The latest in The Conjuring series, subtitled The Devil Made Me Do It, has recently been released. One of the stories based on the paranormal investigations of Ed and Lorraine Warren, it deals with the 1981 case in which the lawyer of Arne Johnson - accused of killing his landlord - sought to enter a plea of not guilty by reason of possession.

The judge rejected this novel argument for lack of evidence and provability and Johnson was convicted of manslaughter. The "possession" argument was more about lawyerly creativity and the sniff of money than any genuine religious or supernatural experience.

The Amityville Horror (now streaming on Stan) was another of the Warrens' "cases" but became particularly well known through the popular Jay Anson book and the subsequent 1979 movie (that spawned a longrunning cinema, TV and straight-to-video film series, some entries of which have tenuous links to the original).

In 1975 George and Kathy Lutz bought a house in which, they were told, Ronald DeFeo Jr had killed his parents and four siblings the year before. In less than a month the Lutz family fled from the house, claiming odd phenomena including voices and slime scared them away.

No subsequent purchasers reported anything odd (except curious gawkers).

DeFeo's defence lawyer, William Weber, said the haunting was a hoax he and George Lutz had concocted: the Lutzes' subsequent lawsuit against him was dismissed.

William Peter Blatty's novel The Exorcist was inspired by reports of a 1949 exorcism performed on a teenage boy. Blatty changed the kid's gender and upped the ante on the horrific stuff in his book and his script for the 1973 film.

More sober analyses debunked or cast grave doubts on most of the claims made about the boy, who might better be described as mentally ill and/or mischievous rather than possessed. With this film and The Omen (1976, now streaming on Disney) - which made no claims to being a true story - many accidents and unexplained incidents were reported as having taken place during production, though how much of this was simply coincidence, carelessness, mundane or the work of an imaginative publicity department is hard to know.

Even when there's no supernatural element alleged, it can be tricky to sort fact from fiction. I don't know if Ed Gein (1906-84) is the serial killer who's inspired the most movies, but he's certainly been popular, and interestingly some of the ones that took looser inspiration rather than any of the ones purporting to be biopics are the best known. His exploits are not for the squeamish. Suffice it to say he was very close to his mother and had some outre ideas about decorating, clothing and women.

Psycho (1960, now streaming on Stan), based on Robert Bloch's novel rather than Gein directly, has the mother-fixated Norman Bates (Anthony Perkins) as a taxidermy-loving hotel keeper whose invalid mother is murderously unhappy whenever he shows any interest in young women. You have to feel sorry for the guy, which is much easier with Perkins than Vince Vaughn in the terrible remake.

The Texas Chain Saw Massacre (1974) drew on some of Gein's grislier activities including the creative use of body parts for decoration and clothing. The serial killer Buffalo Bill in the adaptation of Thomas Harris's novel The Silence of the Lambs (1991, streaming on Stan) also had aspects of Gein (who made himself a female skin suit) as did the lead character in the lesser-known Deranged (1974).

Rumours and embellishments and a desperate desire to believe can add dubious spice to stories. The case of the Cottingley Fairies, while not scary, saw deception meet with credulity for decades. In 1917, young Frances Wright was staying with the family of her older cousin Elsie Wright, 16, in Cottingley, Yorkshire. The girls borrowed the camera belonging to Elsie's father Arthur to prove their claim of seeing fairies nearby. He dismissed the resulting photos as a prank but his wife Polly in 1919 showed them at a Theosophical Society meeting where they were believed to be real, including by leading theosophist Edward Gardner. They came to the attention of Sir Arthur Conan Doyle who, more gullible than his creation Sherlock Holmes, was also convinced.

Some who saw the photos were sceptical - in one publication it was perceptively written, "For the true explanation of these fairy photographs what is wanted is not a knowledge of occult phenomena but a knowledge of children" but the girls stuck by their story for decades, only admitting the hoax - done with drawings on paper - in 1983. They did, however, claim they had seen fairies and Frances rather unconvincingly insisted the last photo was real, perhaps trying to retain a shred of credibility in an affair that had spun out of the girls' control. All this inspired the ambiguously titled FairyTale: A True Story (1997) which tried to have it both ways as to the existence of fairies. Another film the same year, Photographing Fairies, was based on a novel inspired by the same incident.

Enjoy supernatural movies, if they're your thing, but take any claims of veracity with an even bigger helping of salt than usual. And even those based on more mundane reality might not be especially true stories.