Fran Greene is the CEO of two very different companies, Cakes Across America, which sells about $100,000 worth of cakes nationwide, and Sun State Electronics, a $4-million manufacturer of integrated circuits. But from her headquarters, in Winter Springs, Fla., she maintains equally strong vigilance over both companies' accounts-payable systems. "You'd be amazed at the range and frequency of errors I've seen, between my two companies." Errors of $100 to $200 are typical, but Greene has also spotted whoppers as high as $4,000.

Cakes Across America's payables seem, "at first glance, as though they should be problem-free, since we're making only one type of purchase: buying cakes from bakers across the country," Greene explains. "And we pay for 80% of them with our corporate credit card."

Still, "we monitor every single credit-card statement that comes in," she says. "Before we'll make a payment, we double-check each baker's billing against our own internal records about the order -- going over each statement cake by cake, city by city, penny by penny."

All that diligence pays off. "We find errors on 5% of our billings -- not because of any malicious intent, but because mistakes really do happen." For a start-up, the CEO emphasizes, "overpaying that 5% might have been fatal."

Financial experts frequently focus on the risks companies face internally from unsupervised accounts-payable systems (from unscrupulous staffers, for example, who might set up fake payment schemes). But Greene believes that growing companies are equally -- if not more -- vulnerable to problems that originate outside the company.

At Sun State Electronics, Greene's staffers have received invoices from suppliers charging prices different from those quoted at order time. "Or we'll get charged sales tax even though our purchases are entitled to be tax-free when we act as a certified reseller." Errors on interstate shipping charges abound. "Often mischarges are relatively small, but three or four over the years were large."

Because her companies are quite different, Greene has individualized their accounts-payable precautionary systems. At fledgling Cakes Across America, "one person writes the checks and verifies credit-card statements" but must coordinate the work with the accounts-receivable staffer. "So no one person is responsible for the money coming into and going out of the company. And we keep elaborate paperwork records of every order."

At Sun State Electronics, where the financial staff is larger, monthly payables can stretch as high as $250,000, "but each invoice is still verified on a line-by-line basis," notes Greene. "And I personally monitor every payment that's made."

When errors are found, Greene steps in and makes a friendly telephone call to the vendor. "They're often entrepreneurs themselves, and they respond the way I would -- by being grateful that I'm bringing a mistake to their attention that they can investigate and correct as quickly as possible."