Directly and indirectly, it is Kathy Spencer who gave birth to many of those vampires. Annemarie Guertin took Spencer’s class four months ago and says she has since used her system to get more than $15,000 worth of products for little or no money. A 34-year-old kindergarten teacher from Haverhill, Guertin walked out of Rite Aid with so much “free’’ toilet paper that she could not fit it all in her sport utility vehicle; she gave the rest to strangers in the parking lot.

“When a newbie couponer is birthed they are very much like baby vampires,’’ Feehan wrote on her popular blog, The Coupon Goddess. “They go on a couponing rampage that wreaks havoc at every store they descend upon . . . Carnage.’’

“It was the day that sent a seismic wave through coupondom,’’ said Melanie Feehan, a veteran extreme couponer who arrived at a Rite Aid near her home in Plymouth shortly after it opened, only to discover the toilet paper had been cleared from the shelves by a man who bragged to a clerk that he had already emptied three other Rite Aids that morning.

On that seminal Sunday last month, a combination of factors collided to bring an entirely new pack of extreme couponers to the scene at once, unable to resist that first taste of “free.’’ After the Great Toilet Paper Rush, nothing would be the same.

Spencer’s approach requires significant planning and effort, a willingness to stand up to hostile cashiers, and, some say, a lack of shame. But the reward she offers is too good for her thousands of devotees to pass up.

In the world of “extreme couponing,’’ Spencer, a 41-year-old mother of four who lives in Boxford, has quickly risen to guru status. In private classes and a new book, “How to Shop for Free,’’ the woman who claims to feed her family on $4 a week and is known to her disciples as the “Oprah of couponing’’ teaches a complicated, and some say controversial, series of tips and tricks. Her program ranges from simple advice on where to find good coupons and sales, to the calculated exploitation of loopholes in store rewards programs. This is a woman who makes $20 each time she fills a prescription — by moving them to a different pharmacy each month to earn the gift cards that many offer for new or transferred prescriptions.

As soon as Kathy Spencer walked into the Rite Aid in Haverhill, early one recent Sunday morning, she knew something was up: All the carts were gone. At that hour, she was accustomed to having the store to herself, quietly piling hundreds of dollars worth of goods in her cart, quietly working the system, quietly walking out the door without having to pay for any of it.

Using one of the signature techniques of Spencer’s system, they could “roll’’ store credit to get an unlimited amount of toilet paper for free without even needing a coupon. Four-packs and single rolls of toilet paper were on sale for $1, but each purchase earned a $1 reward in store credit. By breaking the purchase up into several transactions and rolling the credit from one to the next, they could essentially make Rite Aid pay for it, over and over.

In December, shortly after the publication of Spencer’s book, the TLC cable network aired “Extreme Couponing,’’ a special that tracked four couponers as they made some ridiculously large hauls. The show triggered a stampede to Internet coupon forums by people desperate to learn the secrets and, on Spencer’s forum, they found an easy way to build stockpiles of a staple that never spoils: Rite Aid toilet paper.

On her website, howtoshopforfree.net , Spencer and her followers — her site received about 43,000 unique visitors last month, according to Nielsen Online — stalk the circulars and wait for moments when a sale can combine with a coupon or two to make the item free or, in a lot of cases, earn them a profit in store credit or rebates. Then they pounce and stockpile the item so they can cross it off their shopping list for an extended period. Spencer’s claim of a $4-a-week grocery bill inspires incredulity, but she says she can do it because she has so many staples in her stockpile, and they only eat what’s on sale. Her husband, Brian, a gravedigger in Peabody, refers to weekly sale circulars as his “dinner menu.’’

Her bargain-hunting chops have become urban legend. People clap for her at the checkout counter. When she took “Good Morning America’’ to her local Shaw’s and used her methods to get $267 worth of groceries for a penny, a stunned Diane Sawyer declared that Spencer made her feel “inferior.’’

In social settings, Spencer is quite reserved, even retiring. She has a small voice and a small frame and admits to being shy almost everywhere except for the aisles. But when she enters a store, she enters a zone; on a recent shopping trip, her pace quickened the second her hands touched the cart. Her eyes scanned everything, and she mumbled aloud as she considered the math for each deal. When she passed other shoppers carrying coupons, she instinctively scrutinized their carts for clues to deals she might be missing. Her husband calls her the “Rain Man of couponing.’’

Coupon redemption has experienced a sharp uptick in the down economy, with six quarters of double-digit growth since 2009, according to Inmar, a company that tracks coupon trends. Within this return to frugality, Spencer is trying to position herself as a penny-pinching brand.

She has similar systems at Shaw’s, Market Basket, Kohl’s and especially CVS , where she has a PhD-level understanding of its ExtraCare rewards program.

“I started at CVS six years ago with $8 out of pocket and since then I haven’t spent any real dollar bills in the store,’’ she said, though she claims she has taken thousands of dollars in real products out. Store managers in her area, wary of running out of sale items, now ask for her help. They give her circulars weeks in advance so she can identify the weak spots and they can stock up.

“She is just very, very proficient at what she does, and I don’t want to run out of things on the first day of the sale,’’ said Wayne Lamoureux, manager of a Rite Aid in Haverhill.

Spencer insists she is not a shelf clearer and preaches against it. But not all her disciples listen, as became clear that Sunday and again the following Saturday, when she took a Globe reporter to Shaw’s.

On her shopping list were four items that had gone on sale a little more than an hour before. With coupons, she could get them for nothing. But in each case, she arrived to find shelves that had been ransacked.

“This is definitely the work of someone who reads my website,’’ she said, chagrined. Several times, she blamed her “big mouth.’’

Spencer first opened her mouth about couponing five years ago, when she used coupons to get three bottles of juice completely free. Her husband was very sick and out of work, and she turned to coupons to help make ends meet. She had grown up in a frugal home in Chelsea with a mother who had an accordion coupon file, but said those three juices triggered an epiphany.

“When I was loading them into the carriage, it all clicked,’’ she said. From there, she “cracked the code,’’ which allowed her to quit her job as a loan officer to coupon full time. After tiring of repeating her instructions over and over, she created a Yahoo! forum and posted her system there. After the site was featured on the Yahoo! homepage, the media came calling and everything took off.

There is an inherent thrill built into extreme couponing, practicioners say, a “coupon high’’ that can be as addictive as a drug. “I’ll bring girls and they’ll just shake like they’re shoplifiting,’’ she said.

Spencer has been doing it so long now and so often — one television show looked at her numbers and estimated that she saves $60,000 a year — that “free’’ has lost its excitement. It’s become a job. She spends a lot of time getting things she does not want or need because it allows her to roll store credit (which expires) or feed her new high, which is giving things away to those who do need it. She says she regularly donates to food banks, and recently made a man cry when she gave him a chicken she had gotten for free.

Extreme couponers love to post photos of their stockpiles online; to the unaccustomed eye, they can be shockingly large, filling multiple rooms. Spencer’s own stash is relatively small; she limits herself to a year’s worth of a product at a time because she’s confident she can always get more.

But, Spencer admits, there is one thing she hoards almost helplessly, and led a reporter to a bathroom upstairs in her house. There, she opened a door to reveal a closet full of toilet paper.

Billy Baker can be reached at billybaker@globe.com.

© Copyright 2011 Globe Newspaper Company.