Regrets, almost everybody's had a few, especially when it comes to shopping decisions. Not just the garish tie that seemed so right for Uncle David but how much that tie cost can really tangle a shopper up inside.

This year, the mental calculations could get really agonizing as discounting has intensified while retailers scramble to clear out inventory that they ordered before the stock market went into free fall, unemployment began rising and consumers sharply reduced spending.

And, tomorrow, the after-Christmas sales begin.

The problem is that retailers can end up inadvertently knotting up consumers in uncertainty if they don't wield their discounts, buy-one-get-one-free deals and one-day sales with care, according to research out of the University of Miami in Florida.

It turns out that consumers who miss a big sale -- and are aware of it -- may decide not to buy at all if they have to pay more for the exact same item, according to research from Michael Tsiros, an associate professor of marketing at the University of Miami, Fla.

Even if the item is still what they want, shoppers don't want to feel bad about their spending choice. "People have this tendency to find ways to regulate this regret," said Dr. Tsiros, whose most recent study on the subject will appear in the Journal of Consumer Research in the spring.

Yet, if given even a slightly different offer that makes comparisons harder, they can pretty easily rationalize the decision, he said.

Chains such as Macy's, Kohl's and J.C. Penney constantly switch up sale items or tinker with the exact offers, as anyone who checks the newspaper fliers or the e-mailed ad pitches may have noticed. They've also moved toward selling more private label products that are harder to directly compare with something sold by another retailer.

That may not help the consumer trying to make a straight price comparison, but it can offer some cover for those looking for a way to feel good about their purchasing decisions.

The more differences, the more tools available to a shopper trying to make a case that the purchase is a smart one. "I think that all [retailers] are not as sophisticated about things they can do to make it noncomparable," said Dr. Tsiros.

In his research, he tested participants' levels of "anticipated regret." In one case, they learned a $500 leather jacket they wanted had been on sale for $350 but they had missed the sale. In another, they were told they'd missed a sale on a sofa they wanted.

When offered a deal on a similar product, participants suddenly found the second choice more attractive and trendy. That was true even no matter which of the two items was shown first.

"They want to justify it," said Dr. Tsiros. "If you can help them justify it, it will make it so much easier for them."

That may mean putting a slightly different model cell phone on sale from week to week. Or a retailer could, say, offer a straight discount on one laptop this week, then next week give a smaller discount but also throw in a $10 gift card.

Dr. Tsiros believes that regret -- and the need to try to avoid that painful emotion -- play a part in many decisions that people make. Many seem to keep a sort of mental account and try to reconcile things as best they can.

If, say, they miss a big sale on a plasma TV, they transfer their need to find a good deal to a discounted digital camera. Or a full-price purchase of one item may be rationalized by a deep discount discovered on something else.

Once a decision is made, the opportunity to feel regret hasn't ended. A shopper may either watch the sales for evidence of his coup or he may avoid sales fliers showing prices would have fallen further had he just waited a little longer.

Both behaviors could be popular during the coming week between Christmas and New Year's Eve, as will the pressure not to miss out on the newest really, really big deals. Of course, this year the fear of regretting spending too much money may carry more weight than usual.

The International Council of Shopping Centers earlier this week predicted December sales would drop 1 percent or more for the industry as a whole, another sign that this will be one of the slowest holiday sales seasons in years.