I sold my bizarre true-life story!

If your orgasms were "so loud you got an Asbo", your pet snake had "eaten your mum", or your "pussy was on Question Time", your first instinct might not be to shout about it.

Yet thousands do, and millions more lap up "true-life stories" like these with the thirst of a missing cat (the pussy, if you were at all confused, was an errant tom called Tango who strayed in front of the BBC's cameras).

From the print equivalents of the Jeremy Kyle Show – magazines such as Love It!, Real People and Take A Break – to the loftiest Sunday supplements, "triumphs over tragedies" and "womb tremblers" (to use the vernacular for anything scary involving pregnancy or babies) are read by an estimated 7 million people a week. The burgeoning market for stories about the extraordinary lives of the ordinary man on the bus or lady upstairs is buoying a floundering magazine industry, and reveals much about the new confessional age into which we've sailed. But what motivates someone to admit that their "best friend is a cannibal" or that their baby "looks like a snail"? Who writes these stories and their often preposterous headlines – and are they true? Cutting Edge: My Daughter Grew Another Head and Other True Life Stories, screened on Channel 4 this week, lands a fly on the wall of an often weird world in which writers, researchers and cheque-wielding agents race to discover the next big exclusive.

Henry, from Essex, was the first man in Britain to have buttock implants. He hated his flat, skinny bottom but didn't have £7,000 to blow on surgery. So he approached an agency called Talk to the Press.

Launched two years ago by freelance journalist, Natasha Courtenay-Smith, the London firm receives more than 20 emails a day from people with tales to tell. Courtenay-Smith sold the buttock story to the Sunday Mirror and New! magazine and is seen in the documentary talking to Henry about a follow-up. As the narrator puts it, "For everyone involved, Henry's bottom has become a goldmine."

But how much do you get for a story about your behind? "Henry made about a grand," says Courtenay-Smith, whose agency received roughly the same amount. "It's hardly a gold mine when you think those implants cost about £7,000."

Indeed, Courtenay-Smith says that subjects can be rewarded with as little as £300 for, say, a weight-loss story, and that money "isn't why most people talk".

Sam Harris is a mother from south London whose son, Nathan, weighed 17 stone by the time he was 12. When she saw a family in a similar predicament on daytime TV, she was moved to bare all. "Nathan was born with a congenital heart defect and has had four major operations," Harris, 34, says on the phone. "He wasn't able to go to the park or do normal activities and I would comfort him with food. He has been bullied and victimised his whole life and I felt judged. I also feel responsible, but I wanted to show there are reasons why people get fat – I wanted them to understand." Courtenay-Smith sold Harris's story to Closer magazine ("I'm Killing my Son with Love"). "We were stopped by a woman on the street," Harris recalls. "She wished Nathan good luck, rubbed my arm and said, 'Well done'. It meant so much."

Harris's story is an example of what might be called "real" true-life stories. Angela Epstein is a journalist and founder of the Manchester-based agency, Sell That Story. She has worked with, among other subjects, the parents of two boys killed in a crash involving the former Plymouth goalkeeper, Luke McCormick (who was jailed for seven years in 2008). "You can sell as many silly stories as you want; but I, and a lot of readers, are more interested in awful things happening that come and hit you in the face," she says. "That's real life. But sometimes the industry forgets because it's so bogged down in the quirky and the bizarre."

It's the sensational end of the market that, for many, defines the trade – and leads to the most criticism.

Hannah Duguid is a freelance journalist who specialised in true-life stories for four years. She appears in the film as the voice of the darker side of the industry (although she reveals more on this page than in the documentary).

"I found it very difficult feeling like a voyeur intruding on people's lives," says Duguid. "I was doing stories told by vulnerable people that, often, I could see no good reason to write about. And sometimes they were complete fabrications. I've had things rewritten by an editor to be completely false." It's standard in the true-life story industry to read articles to subjects over the phone before they are printed, but Duguid – who has since left behind the true-life world to write for newspapers including The Independent – says this courtesy was open to abuse. "Quite often – and I admit I did this – you would read really fast or even skip over the bad bits." Courtenay-Smith says all stories that pass through her office are fully fact-checked and her clients are given every opportunity to approve copy.

Whether they're dressed-up and sensationalised, or important and genuinely affecting, all these stories arguably hold up a mirror to modern society, reflecting a new trend towards openness. "Where once we gossiped over the garden fence, we now read magazines," Courtenay-Smith says. "People are getting used to confessing, and when Gordon Brown has to go on television to talk about losing a baby, it's exactly the same thing."

The story about the mum-eating snake, by the way, turns out to be only partly true: the python bit its prey but was then fought off with a cheese grater.

Cutting Edge: My Daughter Grew Another Head and Other True Life Stories is on Channel 4 on Thursday at 9pm.