From hidden cameras to scented carpets, the rag trade has a string of secret tricks to part you from your cash.
August: a month of damp armpits and dead air. But the woman entering the shop smiles. Face up, neck craning, she drinks in the cool air cascading from above. Relaxed and refreshed, she turns right, just as a casually dressed male assistant says "Hi".

Ahead are tables with fashion's latest must-haves - embroidered tops, suedette skirts, ponchos. They're folded but casually, so she doesn't mind opening them. Anyway there's a customer already hard at it, rummaging through as she chats to the assistant about the tops. "From India," he tells her. "Hand-stitched, but by women who run their own co-operatives."

India, hand-stitched, co-operatives ... the words make her feel good, and she thinks, yes, I might have one of those. She earmarks it and walks on, past tables with similarly displayed merchandise that bounce her into the depths of the shop like angled slides on a pinball machine.

She doesn't see it like this, of course - nor does she realise that the mirrors arranged along the aisles slow her pace, nor that the coffee smells drifting around her serve to perk her up. She likes this shop with its wide aisles - they've even hung the merchandise facing out which is so convenient. And when she finally selects something to try on - helped by the store's style consultant - she can't believe how spacious and softly lit the changing rooms are; there are free make-up samples she can take away and easy chairs outside, with magazines. Here's that style consultant again with more things she can try on - how thoughtful.

Well, it's certainly that, but not in the way that she thinks. What this woman is actually experiencing is a highly evolved psycho-selling technique designed by retail anthropologist Paco Underhill for one purpose and one purpose only: to make her spend more. Using clipboard trackers and time lapse video, Underhill has taught retailers such as Levi's, Calvin Klein and WalMart, owner of Asda, how to turn rag-trading into a canny meta- science. Now Underhill's influence is spreading to Britain - he was spotted recently in ailing Marks & Spencer (which naturally refused to comment on his presence) and his book, Why We Buy, has become a bible for fashion retailers here.

Every little detail in the shop is thought out in minute detail to coax the pound out of your pocket. That blast of cool air encountered at the entrance is part of what Underhill calls the Decompression Process - chilled air to help you think chilled thoughts and soften you up. Next comes the Decompression Zone - that clutter-free space (known as foyer to you and me) whose purpose is to ease you into the main shopping experience.

From here, like our hypothetical shopper, you turn right - the Invariant Right, researchers call it. Since most of us do it instinctively, the best and most expensive fashions are located here, along with the things that create those all-important first impressions: the greeter, that table.

The greeter helps to relax you into the shop; the table or Power Display sets out its ethos - hip fashions at buy-now prices. The Power Display is also known as the Lure, or the Come-On because it is designed to reel you deeper and deeper into the store. Even that sloppy folding is deliberate - Underhill and his cameras have shown that neat folds make customers nervous and discourage them from exploring even further.

Angled tables coax you further into the shop and mirrors in the aisles keep you moving slowly but carefully along a pre-determined route (the Race Track), from which off-aisle hives have been created to make it easier for sales staff to target you. Twinkling accessories and rotating displays with reflective surfaces are used to lure you into places you had no intention of going.

Towards the back of the shop we find the first of what retailers call Fashion Black Spots - places with low foot traffic. The shop tries to draw you into these areas and one trick is to put the escalator here - apparently we can't resist going up one of these (but try to find the down escalator when you get to the top) - but there are others, such as Points of Theatre (elaborate displays) and the everything-less-than-a- tenner rail approach. Wallis is good at this, as is Monsoon, Accessorize, and Debenhams. Indeed Debenhams has made a fetish of it, salting designer names in among the pap so that fighting through all that polyester and Women's Institute burgundy seems worth it. Retailers in the US cynically call this the 'carrot and stick' effect. It explains why designer fashion is never shown on the ground floor but one or two floors up, or six or seven rails back.

Into the changing rooms, traditionally a place of torture for many women as they see just how bad their bodies look in this season's clothes. But not any longer. Shops have used tinted glass mirrors to make us look tanned for years; now they are using convex ones to make us look slimmer. The Key-Hole Effect, as it's known, is already doing the rounds at retail trade shows up and down the country.

Make-up in the changing room, easy chairs outside it, and style consultants - these are all good tricks, particularly the style consultants. At Harvey Nichols, Selfridges, Dickins & Jones, Marks & Spencer, they are nothing more than sales staff, there to flatter you into buying things you never wanted. They call it customer care or, better still, Holistic Retailing, but the retail psychologists have a better phrase for it - Love Bombing.

And that guff about hand-stitched embroidery and workers' co-ops? It's just to convince you that the shop has ethics. Research shows that customers are better disposed towards ethically aware shops so ... well, you get the picture. According to Chris Dawson of retail consultancy Management Horizons Europe, it's known as Cause Related Marketing, another way retailers are getting us to see them in a better light. "It's a good way of flagging up a company's ethos, of showing that they care. And by buying into this we feel we are showing similar attributes."

It also raises PR profile, as Tesco proved recently by sewing details about testicular cancer into men's boxer shorts. Marks & Spencer and Rigby and Peller have done similar things with bras and breast cancer. Even a streetwise label such as Komodo does it with tags telling you how much of its profits go to its Save Tibet fund.

But the hustle doesn't stop there. Note how shops are displaying fewer garments and making aisles wider, and it's not to make room for your pushchair. This is what Matthew Jeatt of trend consultancy Promostyl refers to as the Space/Luxury Equation. "Research shows that we now measure space in terms of luxury or quality. That shops with a lot of space and fewer garments are perceived to be luxurious. Indeed if you hang a single white shirt on a rail, facing out, and leave space around it, people think it's worth more than the same shirt on a crowded rail."

Wider aisles also counter what Paco Underhill calls the Bum-Brush effect. Over and over, his cameras recorded images of women in narrow aisles bolting when their bottoms were pushed up against - and sales in that area went down. In Bloomingdales, where the phenomenon was first noted at a tie rack, aisles were widened and stock given more space. The result? Sales rose by 30 per cent.

Expect more space than ever - and more of those deep-pile customer hospitality areas or merchandise cul-de-sacs which shops such as Hennes, Harvey Nichols and French Connection are pioneering. Catchment basins they are called - cosy little pockets set off the main aisles where lingerie, footwear and career-wear are displayed with coffee, magazines and easy chairs attached, gratis. Harvard scientists Stephen Kosslyn and Gerald Zaltman explain that retailers are creating these chill-out zones because they've discovered that pampered customers not only respond positively to the environment they are in, but also that the heart actually pumps blood to the prefrontal cortex - the part of the brain that makes us want to buy, buy, buy.

Retailers create a similar effect by using the colours that psychologists say make us feel more positive and confident - orange, green, blue, yellow, red or purple. Think Hermes, Ralph, Tommy, Oasis, Selfridges, and suddenly their logos and shop interior colours make sense. Another trick is to circulate artificial coffee, citrus and lavender smells. Promostyl's Matthew Jeatt explains: "Coffee and citrus scents are known to encourage alertness. The car industry at the moment is developing models that spray the driver with citrus essence when his blink rate indicates that he is about to fall asleep. This effect is liked by retailers for obvious reasons; by the time we get to the centre of a store we are flagging, not noticing."

Many stores now have systems that distribute smells via their air conditioning, while others have fragrance-impregnated carpets - even jacquard sweaters that emit fresh alpine smells when you stroke

them. Research also shows that the smell of coffee triggers Cosmopolitan Thoughts - they make people feel hip, plugged in. Selfridges now has coffee bars edging on to its sales floors.

This wooing of the senses, however, can be appreciated best by visiting stores such as Donna Karan, Top Shop or Nike Town. "Welcome!" "Hi!" "How's it hanging?" The plain old "Can I help?" is defunct - we always insist we're just browsing in response to that one, says Underhill. Assistants are now trained to ask questions that invite comment, or as Donna Karan put it, to create "a nurturing environment where you feel that you will be taken care of".

Which you will be, but not in the way you want. Any talk with any assistant, you see, increases the possibility of a sale by as much as 30 per cent, according to Tony Heinz, retail analyst and author of Managing Information for Marketing Decisions, "while the longer you get people to stay in a store the more they will feel guilty about leaving it without buying something". Eleven minutes and 27 seconds is the required time, if you must know.

Top Shop and Nike Town have honed Holding Time tactics into an art form. Top Shop hooks you with its on-tap catwalk shows, make-up demos, table soccer and internet shopping sites, while Nike Town has soundbite blahs from sporting heroes to keep you listening and light displays to keep you looking. It even employs assistants who are professionals in their own right - goalkeepers, runners, golfers, and all trained at conversation so you hang on in there, chatting. Lucky if you're out in 20 minutes, never mind 11.

Notice, too, how women's clothes have become softer lately, more tactile, and how assistants encourage female shoppers to handle the garments they are looking at. Petting, it's called. And the heavier a woman pets a piece of clothing the greater the likelihood is that she'll buy it - 80 per cent more likely, in fact.

Men can't be sold in quite the same way - which doesn't mean they're immune to this voodoo. "Men just shop differently," says Tony Heinz. "Research shows that women are sophisticated, complex shoppers, while men act like children." This is why shops such as Blazer, Burton and Moss Bros corral clothing types together in fail-safe combinations called Adjacencies - they hang jackets next to ties next to shirts. They display ties and shirts that are graded by size and colour like Dulux paint charts so even the dumbest man can't go wrong.

Like kids, men are impulsive. Retailers such as Next play on this by stacking bath and shower kits next to sports tops (sport-sweat-shower) and watch them walk from the store.

They also know that men look at price tags less than women - and yes, and they also equate bigger prices with larger you know whats, which is why male consumers are charged more by retailers and are happy to pay up. More tellingly, says Underhill, "If a man takes something into a changing room, the only thing that stops him from buying it is if it doesn't fit." Which is why men's changing rooms are now easier to find.

"All of these things have happened in other industries," says Chris Dawson of Management Horizons Europe, "and fashion is beginning to catch up - fast. I'm working with retailers who are using imaging software that allows them to call up images of their stores on screen and then to arrange merchandise, fixtures, colours and key focal points to achieve maximum impact with customer sales. These can be tested on focus groups and, if positive, sent down the line to stores where interiors can then be adjusted accordingly."

And the future? Even more techno-centric, says Tony Heinz. "US stores like WalMart are already selling garments containing washable microchip implants that can store or transmit information and, in tandem with the retailer's electronic point of sales systems, be used to create a lifestyle database of customers as they move through a store. So retailers will be able to anticipate your likes and dislikes, and provide their staff with even better chat-up lines to seduce you with."

Imagine our fictitious shopper again, entering the store, decompressing, browsing, not knowing where she is going or what she is looking for. But the greeter does. On screen, our shopper's profile has been activated. Name, rank, cereal choice. "Ruth, good to have you back with us - how about a new top to go with those trousers you bought? Oh, and we've had a new delivery of bags, really fab ones - I know you went looking last visit but couldn't find anything." Ruth is impressed: in a big shop with so many people, she's been recognised and acknowledged this guy really is like family, a brother. A very big brother.

Martin Raymond is an analyst and lecturer at the London College of Fashion.