TheU.S. Securities and Exchange Commission is examining Groupon Inc. (Nasdaq: GRPN), the world's largest online coupon company by sales, for a revision of its first set of financial results, the Wall Street Journal reported Tuesday.

The SEC probe is at a preliminary stage and a formal investigation has not been launched, a person familiar with the matter told the Journal.

The controversy errupted as the company moved to higher-end offerings, like vacations and Botox treatments that tend to bring higher rates of returns. Groupon, however, failed to set aside enough reserves to account for these increases.

The growing troubles at the Chicago-based company, which was founded in November 2008, are beginning to vindicate three of its long-time critics.

Even before Groupon went public less than five months ago, it was already under the SEC's microscope as the regulatory body raised copious issues with its prospectus filing, noted Chris O'Brien of SiliconBeat, a tech blog.

Last Friday, it announced a revision of its fourth-quarter results, reducing revenues by $14.3 million and net income by $22 million. It also admitted a material weakness in its internal financial controls.

Groupon shares plunged nearly 17 percent in response on Monday.

The problem stemmed from coupon refunds from customers. One explanation is the higher-than-expected rate of returns from pricier deals, such as Lasik eye surgery, which Groupon's previous models did not account for, reported the Wall Street Journal, citing a person familiar with the matter.

Given Groupon's history with the SEC and questionable accounting practices, longtime critics Rocky Agrawal, a tech consultant, and J. Edward Ketz and Anthony H. Catanach Jr., two professors at Penn State University, maintain their skepticism.

We just can't resist: TOLD YOU SO! wrote Ketz and Catanach.

On Aug. 24, they warned investors that Groupon's balance sheet stinks, its income statement reeks and cash flow is in the toilet.

Instead of participating in this IPO, we would rather purchase lottery tickets, declared the professors.

Agrawal, who also started raising issues with Groupon last year, said Groupon's earnings revision surprised me as much as my $2 investment in the Mega Millions jackpot not paying off.

He specifically raised issues with the company's refund reserves, charging it doesn't run risk assessment before offering deals.

For example, if the company does not screen customers for medical procedures, those who don't qualify for the procedure will of course return their unusable coupon.

If Groupon does not address this issue, Agrawal expects refund rates to continue to rise.

Shares on Tuesday fell 1.67 percent to close at $15.02.