Greenberg: Warning Bells at MercadoLibre

Editor's Note: This article was originally published at 11:10 a.m. EDT on Real Money on Sept. 12. Sign up for a free trial of Real Money.

If MercadoLibre ( MELI) doesn't ring a bell, that's because you don't live in Latin America, where it's known as the eBay ( EBAY) and Amazon ( AMZN) of such countries as Venezuela, Argentina and Brazil.

Either that, or you haven't been keeping up with the market's highest of highfliers. The 50%-plus rise in MercadoLibre's shares so far this year -- with a 300% gain since the stock's 2007 U.S. initial public offering -- has earned this name a coveted spot on the momentum-stock hit parade, also known as the IBD 50. Adding to the investor enthusiasm: eBay is its largest investor.

But this head's up: Despite what appear to be the steady blockbuster results of an impressive growth company, a few analysts are starting to raise concerns over such things as increased competition (from the likes of Amazon itself) and decelerating revenue in the company's biggest market, Brazil.

Nothing, however, is potentially more worrisome -- yet largely ignored, overlooked or simply talked away -- than the brewing controversy over the way MercadoLibre accounts for currency translation in countries where currencies are collapsing against the U.S. dollar as inflation shoots through the roof.

The company's loudest critic, Mark Roberts, of the venerable independent research firm Off Wall Street, believes MercadoLibre's foreign-exchange accounting is out of step with Generally Accepted Accounting Principles, or GAAP. He believes that, as a result, the company grossly overstates its sales and profits. "The way they do it is totally inflated and exaggerated," he says. "It has no connection with reality. It's all driven by inflation. The more the inflation, the better the results."

At least one informed company insider, CEO Marcos Galperin, doesn't appear to be taking any chances. On Aug. 8 he sold 293,338 shares at $124.26 a share. This was his first sale in well over a year, and it represents 39% of his direct stock holdings.

Insiders sell for all kinds of reasons, and selling in and of itself is not always a red flag. But, according to George Muzea of Muzea Insider Consulting, in the past Galperin has demonstrated an uncanny ability to sell before MercadoLibre's stock has taken a tumble. "He has top-ticked before," Muzea warns. "Be careful."

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