Rima Pavalko says she "learned the hard way" that Wal-Mart has instituted a tougher policy on merchandise returns when she tried to return a drapery rod recently.

After standing in line for 20 minutes, the Ellicott City mother was told that the store would not take the item back without a receipt. "I had hit the magic limit of three returns without a receipt in a year," Pavalko, a regular Wal-Mart shopper, says the clerk informed her. "I was made to feel like I had broken some terrible law."

Annoyed and embarrassed by the incident, Pavalko wonders how much sense Wal-Mart's longtime 90-day return policy makes now that new limitations on the number of no-receipt returns a customer can make have gone into effect. "You have to keep a receipt that long?" she says. "Who really does this?"

Wal-Mart's policy tweaking reflects a recent trend among large retailers nationwide who are shortening return periods, tightening receipt requirements and even electronically tracking returns to identify frequent returners. The measures are an attempt to reduce the $16 billion annually the industry reports is lost to return abuse.

"Typically, we are seeing mass amounts of merchandise stolen and returned. The problem is the retailers never sold this merchandise to begin with so they're giving away cash," says Ellen Tolley Davis, spokeswoman for the National Retail Federation.

"We're also talking about what may seem like smaller circumstances -- someone purchases a prom dress, wears it and brings it back, or someone buys a laptop, writes a term paper and brings it back, or someone buys a DVD, copies it and brings it back. Obviously those products have diminished value."

So many kinds of return abuse occur that it's difficult for retailers to identify them all -- and distinguish the perpetrators from honest customers who return several purchases.

"Many retailers feel they can look for patterns or they can inspect certain types of merchandise that might be larger targets of return fraud -- for example, costume jewelry. Many retailers won't take it back anymore," says Davis, adding that the cost of return abuse adds to the prices everyone pays for products. "We've seen many retailers changing their return policies to identify and prohibit return fraud in their stores."

But sometimes shoppers such as Pavalko pay a price in the return line because of return abusers. "I'm miffed. I hate collective punishment," she says. "Wal-Mart needs to work a little harder at distinguishing good shoppers from shoplifters."

Wal-Mart spokeswoman Sharon Weber says Wal-Mart still has one of the most liberal return policies in the marketplace. "Generally, we accept returns within 90 days after purchase," she says, mentioning exceptions such as computers and accessories, camcorders and digital cameras -- all of which have shorter return windows. Music, movies and software must be returned unopened.

"Wal-Mart, for several years, has accepted returns without a receipt, even though many of our competitors require receipts for all returns," says Weber.

The new return policy changes only for a customer who has returned more than three items without receipts within a 45-day period, she says. "The cash register system will automatically flag the transaction, and a customer service manager . . . must approve the return."

Dissatisfied Wal-Mart customers, such as Pavalko, should ask to speak to the store manager, says Weber. "Whether it's a return or any other customer interaction, we want our customers to be satisfied."

Jim Hood, founder and CEO of Consumeraffairs.com, a consumer advocacy Web site based in Fairfax and Los Angeles, says retailers' efforts to stop return abuse "is becoming a real hot button."

"Stores are trying to target 'serial returners' by using databases that track how many items a consumer has returned to that store and others," he says, and there's nothing to stop them. Most state consumer-protection laws (including those locally) require retailers only to post return policies that are more stringent than the common-sense notion that a product can be returned with the receipt.

"State laws vary but, in general, stores can do whatever they want, as long as they disclose their policy through in-store postings and notations on receipts," says Hood, adding that Wal-Mart generally has a good reputation concerning returns.

"It's very hard to be a casual consumer these days," he adds. "Every transaction is a battle of wits -- the lowly consumer against a global enterprise loaded with MBAs and lawyers but seemingly lacking any appreciation of the role of the customer."

Got questions? A consumer complaint? A helpful tip? E-mail details to oldenburgd@washpost.com or write Don Oldenburg, The Washington Post, 1150 15th St. NW, Washington, D.C. 20071.