Lean times for internet giant...Yahoo is clamping down on outstanding bills by charging customers on its auction site for fees as low as five cents. The company previously allowed customers listing goods on the auction site to accumulate fees until they reached a certain level. But following a recent upgrade to its billing system, Yahoo has contacted all customers with outstanding balances demanding payment. The company said it did not know how many customers would be affected but said the outstanding amount was not that big. Yahoo's auction site was one of the first services to attract a fee when the company introduced content charges 18 months ago.