Fire your bad customers. That piece of advice has become widely accepted in recent years as companies have sought to manage their relationships with customers in more sophisticated ways. The rationale is clear-cut: Low-value customers end up costing more money than they provide. So why not jettison them and focus your customer-relationship efforts on more profitable individuals? Or as an alternative why not try to increase the worth of the low-value customers to your firm? Not so fast suggests a new study by two Wharton marketing professors -- Jagmohan Raju and Z. John Zhang -- which concludes that firing low-value customers actually decreases firm profits and that trying to increase the value of these customers may be counterproductive.