Groupon, the online deals site that was once the darling of both Wall Street and the Chicago tech scene, continues to stumble. On Monday morning, its stock price fell another five percent—and that came after a 30 percent drop on Friday. The stock has now lost 90 percent of its value since its initial public offering last year.

Last week, Groupon posted a quarterly loss of $3 million which, although far better than last year, has raised fundamental questions about its business model. Its competitors, most notably Amazon’s Living Social, have also been struggling. The main problem: while merchants might be willing to offer a discount to entice new customers once, they aren't always so eager to do it repeatedly.

"A lot of people made the mistake of overlooking the price-promotion part of this model," Utpal Dholakia, professor of management at Rice University's Jones Graduate School of Business, told Reuters. "Normal advertising, yellow pages advertising, it really doesn't have a price promotion, it doesn't have discounting component. That's what makes this difficult to do again and again."

Still, Groupon hopes that it might be able to turn things around with its Groupon Goods division, which is doing far better than the company’s primary deals division.