Every week, 3 to 10 packages of perfume, makeup, CDs and clothes are delivered to the El Paso, Tex., home that Sara Jane Marvel shares with her husband, U.S. Army Capt. Brad Marvel (yup, he’s Captain Marvel), and their two cats.

While Sara Jane is cooing over her new loot, other women from Austria to Arizona are opening packages from Sara Jane filled with the jeans,fragrances and accessories that she no longer wants.

Thrifty Europeans long ago embraced bartering as a brilliant way to maximize scarce resources while avoiding waste, but Americans are just starting to discover the pleasure and profit in trading their homes (cuts down vacation costs!), coupons, gift cards and other goods.

Sara Jane, 25, a high school English teacher, started swapping after a college friend left her with a cache of unwanted makeup and she serendipitously stumbled upon makeupalley.com, a site that lists more than 225,000 items for trade.

Now a veteran of more than 90 swaps, Sara Jane loves the economic efficiency of online trading and “chatting” with fellow fragrance aficionados. Often, she says, the women with whom she trades throw in "extras" based
on the skin care and perfume preferences she has expressed in her online profile.

One of her best swaps? Trading a $25 gift card she knew she would never use for a brand-new $40 sweater from the Gap that she adores. Besides feeling pleased with the exchange, she says, swapping in the mail saved her the hassle of searching for the cozy sweater she yearned for in stores. "It's like Christmas every day here!" exults Sara Jane.

People barter goods and services worth about $9 billion a year with the help of the Internet via two main models, explains Bin Gu, Ph.D., an assistant professor in e-commerce and Internet technology at the University of Texas at Austin.

The first model, used by sites such as makeupalley.com, permits users to locate people who want items they have and folks who have things they want through "swap lists" and "wish lists." Users contact each other via the site's mail service. If a deal is struck through online negotiations, addresses are then exchanged.

The second model works more like a babysitting co-op: On sites such as frugalreader.com, users earn credits or points for stuff they send to others, which can in turn be redeemed for things they want. This model is more complicated and time-consuming, usually more expensive and less popular, Gu notes.

Using the Internet to trade easy-to-send items that aren’t worth selling on eBay makes a lot of sense, says Gu. The too-small coat you bought or that book you will never read "has zero value to you, but to someone else the value could be substantial," he points out.

Of course, you may receive a coveted perfume only to be told by your own superhero husband that he does not find its scent appealing. In swapping, you rarely get "refunds," but, as Sara Jane notes, "you can always swap it again!"