In today's challenging economy, retailers are offering bigger discounts than ever.

But shoppers should proceed with caution before entering a store with steep discounts, according to Mark Ellwood, author of "Bargain Fever: How To Shop In A Discounted World."

"If you see a sign for more than 70% off, strike that retailer from your list of places to shop," Ellwood told us. "Those discounts reveal that the company is badly run, and the store was likely charging too much to begin with."

"It's a huge warning sign, and the customer shouldn't trust retailers who do this," he continued. Discounts in the range of 30-50% are more legitimate, in his view.

American attitudes toward discounting have changed in recent years.

A decade ago, customers would have thought that a 70% discount was absurd, but now they've come to expect it, Ellwood writes in "Bargain Fever."

In 2006, only one in three shoppers found a "70% off" sign credible. But six years later, more than two-thirds of people believed the discount and would shop at the store.

Moreover, the number of Americans who only purchase clothes on sale has gone up to 23% from 15% in 2007.

"The number of discounts today is astounding, but these deals aren't always in the best interest of the consumer," Elwood said.

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