At the start of 2008, Anna Sam, was part of a legion of 170,000 French women who are, in her words, “omnipresent but invisible”. She was a “beepeuse” (a woman who beeps) or, more officially, a “hôtesse de caisse” (till-hostess). In other words, she was a supermarket check-out girl.

In January, Mme Sam, 29, began to write about her experiences, first in a blog, then in a book. She told of life behind the till and the conveyor belt - “one of the most desirable vantage points from which to enjoy the full panoply of human idiocy”. Almost a year later, the invisible woman is not only omnipresent but inescapable.

She has become a best-selling author, with more than 100,000 sales, and a triumphantly successful blogger, with more than 1,000,000 visits to her site (caissierenofutur.over-blog.com). Her advice on the life of shop-workers is sought by politicians and supermarket chains.

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Her book - “Les Tribulations d'une Caissière” (The tribulations of a check-out girl) - is about to be translated into several languages. There are projects to turn Mme Sam's life - literature-student-turned “beepeuse”-turned-author - into a comic-book, a play and a film.

The young Breton attributes her success to a turning away from a stifling obsession with celebrities towards a refreshing interest in the humour - and heroism - of everyday lives. “I talk about things as they really are, without exaggeration or aggression,” she said. “My popularity shows that society is changing more rapidly than we think.”

The success of Anna Sam's book follows in the tradition of other, surprising, runaway triumphs in France in recent years, such as the movies “Amélie Poulain” (2001) and “Bienvenue chez Les Ch'tis” (2008). All three are pleasantly humorous portraits of the lives of ordinary people.

Mme Sam is still determined to extract light-hearted revenge from the thousands of customers who ignored, or insulted her, during her eight years behind the tills of a suburban supermarket in Rennes. “(My book) is so easy to read that even supermarket customers can read it,” she says.

With malicious but gentle wit, she lists the different categories of “typical” customers. There are those who have their noses impatiently pressed to the sliding door 30 minutes before opening-time. There are those who are discovered ambling behind their trolley ten minutes after the doors have closed.

There are the boastful ones, whose trolley contains nothing but extra-size condoms. There are the pathologically bashful ones, who go to extreme lengths to hide toilet paper beneath other items in their trolleys. (If the bar-code happens not to be working, the “beepeuse” takes a malicious pleasure in broadcasting to the whole supermarket a request for the price of “an extra-large packet of pink, double-ply toilet paper”.)

There are also the queue-jumpers, the kleptomaniacs (CDs hidden in camemberts are common in France, apparently) and the obsessive bargain-hunters. There is the orderly young man who places his shopping neatly on the conveyor belt, followed by a piece of snot picked from his nose. There are the customers who keep their money in their socks or their bras.

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And then there are the customers who carry on conversations on their mobile telephones while failing to say “bonjour” to the invisible “beepeuse”.

“But I'm already at the till! Why didn't you tell me that you wanted bananas…You want to go out tonight? But have you stopped throwing up yet? I am sure you have the gastro. I hope you haven't given it to me. I don't want to spend the whole night on the toilet…”

Mme Sam has a special hatred for the male customers who used to ask her “vous-êtes ouverte?” - meaning “are you open?” but also “are you available?” “I am not but my till is,” she would primly reply.

Supermarkets can be erotic places, it seems (French supermarkets at any rate). Mme Sam writes: “You would be astonished by the amount of kisses stolen in the aisles (even in the toilet paper department), the langorous looks exchanged between the charcuterie and fish counters, the bottoms and breasts felt in the frozen food department…”

Mme Sam is especially poignant, however, on the fate of the “beepeuses” themselves, trapped behind their tills, unable to escape easily for a breather, or a coffee, or even a pee.

A check-out girl, Mme Sam calculates, says “bonjour” 250 times a day, “merci” 500 times a day and “have you got a frequent customer card” 200 times. She (and very occasionally in France, he) beeps 20 items a minute and lifts 800 kilos an hour for a monthly salary of €850.

Mme Sam says that, in becoming an author, she looked forward to having more spare time, especially at weekends. Now, she says, she is in so much demand that she “has plenty of time but not a minute to myself.”