Facebook's (FB) early investors plan to sell major stakes in the company's initial public offering this week. Is this a red flag for investors or simply smart business?

After seeing so much investor enthusiasm for the IPO, early shareholders like Accel Partners are boosting the amount of shares they're selling. Accel has raised its amount by 28%, and will now offer more than 49 million shares in the IPO.

Facebook is estimating an IPO price of between $34 and $38 a share (the official amount will likely be decided Thursday). At the midpoint of that range, $36 a share, Accel stands to make nearly $1.8 billion.

Accel will still hold 144.4 million Class A shares and nearly 8 million Class B shares after the IPO. So I don't look at this with the same skepticism as The Wall Street Journal, which says that "the smart money is flying out of Facebook as the dumb money piles in."

I think is a natural move for Accel to reduce its risk -- and take home a whopping check in the process. Does the selloff mean Accel thinks Facebook will drop like a stone? Of course not. If Accel really thought that, it would be cashing out a lot more.

Goldman Sachs (GS) is dumping a much bigger stake. Facebook's latest regulatory filing shows that Goldman will sell 28.7 million shares, or about 43% of its holdings.

Venture capitalist Peter Thiel will sell 16.8 million shares, pocketing about $606 million. He's holding on to nearly 19 million Class A shares and 9 million Class B shares.

Facebook's CEO isn't increasing the 6% of his stake he had already planned to sell.

At least one investor said all of this investor dumping could be viewed badly. "When you see insiders unloading their stakes, you start to wonder why," one chief investment officer told Bloomberg. "I could see it turning some institutional investors off."

Facebook and its existing holders have increased the total shares offered in Thursday's IPO to 421.2 million from the previous 337.4 million. The deal's underwriters also have the option to buy as many as 63.2 million more shares after the IPO.

At the high point of Facebook's estimated IPO range, or $38 a share, Facebook would raise slightly more than $16 billion. That would be the second-largest IPO in U.S. history, Bloomberg reports, behind the $17.9 billion raised by Visa (V) in 2008.

Compare this with other tech IPOs, which didn't see nearly the same amount of early selling, writes the Journal's Rolfe Winkler:

Another interesting wrinkle is the comparison with previous tech IPOs. At Groupon, insiders and early investors didn’t sell any of their stake in its IPO. LinkedIn’s IPO similarly saw very little selling. At Zynga, insiders and early investors sold just 7% of their stakes on average.

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