If only we could have spotted the rascals ahead of time. That's the lament of anyone who bought Enron stock a year ago, or who worked at a now-collapsed company like Global Crossing or who trusted any corporate forecast that proved way too upbeat. How could we have let ourselves be fooled? And how do we make sure that we don't get fooled again?

It's time to visit with some serious cynics. Some of the shrewdest advice comes from Wall Street's short sellers, who make money by betting that certain stocks will fall in price. They had a tough time in the 1990s, when it paid to be optimistic. But it has been their kind of year. Almost every day, new accounting jitters rock the stock market. And if you aren't asking about hidden partnerships and earnings manipulation -- the sort of outrages that short sellers love to expose -- you risk being blindsided by yet another business wipeout.

Think of short sellers as being akin to veteran cops who walk the streets year after year. They pick up subtle warning signs that most of us miss. They see through alibis. And they know how to quiz accomplices and witnesses to put together the whole story, detail by detail. It's nice to live in a world where we can trust everything we're told because everyone behaves perfectly. But if the glitzy addresses of Wall Street have given way to the tough sidewalks of Mean Street these days, we might as well get smart about the neighborhood.

The first rule of these streets, says David Rocker, a top New York money manager who has been an active short seller for more than two decades, is not to get mesmerized by a charismatic chief executive. "Most CEOs are ultimately salesmen," Rocker says. "If they showed up on your doorstep and said, 'I've got a great vacuum cleaner,' you wouldn't buy it right away. You'd want to see if it works. It's the same thing with a company."

A legendary case in point involves John Sculley, former CEO of Apple Computer. In 1993, he briefly became chief executive of a little wireless data company called Spectrum Information Technologies and spoke glowingly of its prospects. Spectrum's stock promptly tripled. But those who had looked closely at Spectrum's technology weren't nearly as impressed.

Just four months later, Sculley quit, saying that Spectrum's founders had misled him. The company restated its earnings, backing away from some aggressive treatment of licensing revenue that had inflated profits. The stock crashed. The only ones who came out looking smart were the short sellers who disregarded the momentary excitement of having a big-name CEO join the company. Instead, those short sellers focused on the one question that mattered: Are Spectrum's products any good?

So in the wake of Enron, you want to know what to look for in other companies. Or, more to the point, you need to know what to look for in your own company, so you're not stuck explaining what happened to your missing 401(k) fund. Here are six basic pointers from the short-selling community.

1. Watch cash flow, not reported net income. During Enron's heyday from 1999 to 2000, the company reported very strong net income -- aided, we now know, by dubious accounting exercises. But the actual amount of cash that Enron's businesses generated wasn't nearly as impressive. That's no coincidence.