Wal-Mart uses various methods to control the quality levels of its suppliers, including linear averaging and ABC analysis. The company's purchasing analysis focuses on reducing costs and providing best prices in the market. Linear averaging method is used to evaluate suppliers based on performance, quality, delivery time, and cost, while ABC analysis categorizes items into three categories: A (15-20% of inventory value), B (30-35% of inventory products), and C (50% of actual items but only 5% of the inventory value). The company's strategy is to sell more products at less profit, which has helped it grow and become a leading retail brand.