If you follow growth stocks, small-cap stocks, China stocks, or some combination of the three (small-cap China growth, anyone?), chances are you noticed earlier this month that VisionChina Media (Nasdaq: VISN) closed down almost 50% -- and it's dropped further from there.

When a stock drops that much, it gets my attention. That's because dumpster-diving can be a very profitable activity. Consider that while Ford (NYSE: F), Advanced Micro Devices (NYSE: AMD), and Mercadolibre (Nasdaq: MELI) all dropped more than 50% in 2008, they more than tripled in 2009.

It is not, however, a sure thing. Citigroup (NYSE: C), General Electric (NYSE: GE), and Valero (NYSE: VLO) were down big in 2008 and went right on dropping in 2009.

So what's the outlook for VisionChina Media? And is it a buy?

Meet our contestant
VisionChina's business, in which it distributes television content and advertising to buses and subways in China, was appealing to investors for a number of reasons.

First, it was fast-growing. Sales were up more than 250% in 2008 and more than 70% through the first half of 2009. Second, it was capital light, with operating expenditures checking in at less than 20% of sales in 2008. Third, it had a strong balance sheet with more than $100 million in net cash. Finally, it was wildly profitable, with better than 60% gross and 40% operating margins in 2008.

All of this propelled the stock up to more than $20 per share. Then, however, the advertising market in China began to weaken and Vision's results began to suffer. The stock was trading for less than $10 at the beginning of this month and closed yesterday at less than $5.

What happened
As advertising rates drop in China, Vision's sales are slowing and profit margins are narrowing. In fact, sales were up just 3% in the fourth quarter and the company's gross margin dropped to 45%.

This problem was compounded by the company's decision to purchase DMG Media, the operator of digital mobile TVs in the Shanghai subway system, for $160 million in cash and stock. That move dramatically increased the company's fixed costs and weakened its balance sheet at a time (the present) when it doesn't look prudent to have done either of those things.

All of this resulted in the company issuing first quarter 2010 guidance of "no less than $22 million" in sales, and analysts suggest that portends a significant net loss. Put it all together and VisionChina is no longer fast-growing, no longer has a strong balance sheet, and is no longer wildly profitable. So you can understand why the market has soured on the stock.

So is it a buy?
My problem with VisionChina's guidance is that by my estimate it implies a near 50% drop in the rate it charges advertisers. We all know advertising is a cyclical industry, but that's a pretty violent decline.

Further, it's unclear where the rate will settle out as the advertising environment rebounds in China. While the company's networks in Beijing and Shanghai are premium assets that should command premium prices, the company's network growth has largely been in tier 2 and smaller cities such as Harbin and Chengdu.

The fact is that consumers in these cities are not nearly as wealthy as those in tier 1 cities such as Beijing and Shanghai and therefore not as attractive to advertisers. As a result, they will drag on the company's average rate. Yet it's the magnitude of that drag that is so difficult to know, and any valuation of VisionChina will vary widely depending on our ad rate assumption.

If we believe in the Chinese consumer and that industry consolidation will lead to Chinese companies trying to build well-known nationwide brands in China, then we would forecast a brisk advertising recovery in all markets -- and should buy VisionChina stock at today's prices even if we have to ride out a rough first quarter.

If, however, we believe that it will take a much longer time to bridge the gap between China's rich and poor, then VisionChina's stock still doesn't quite look like a bargain.

There are no called strikes in investing
I'm holding off on VisionChina for now and continuing to gather information. My thesis is that the best performing part of China this year will be rural China, and that tier 2 and tier 3 cities will continue to struggle given all of their excess capacity in real estate. That would mean a rough ride for VisionChina, its ad rates, and its investors.

If, however, I got your attention with my rural China thesis, then I encourage you to check our Motley Fool Global Gains special report The China Rural Boom Basket: 5 Ways to Play the Fastest-Growing Niche in China. It's free to download from our website with a free, 30-day Global Gains guest membership. Just click here to get started.

Tim Hanson is co-advisor of Motley Fool Global Gains. He does not own shares of any company mentioned. Mercadolibre is a Motley Fool Rule Breakers recommendation. Ford Motor is a Stock Advisor pick. The Motley Fool often anthropomorphizes its disclosure policy, but that hurts its feelings.