Even after having signed a supplier contract, large retailers like Wal-Mart are almost never compelled to buy anything, and their purchase orders may or may not follow. Large retailers also usually ask smaller suppliers to guarantee that their product will sell. What sets a small supplier apart is its innovativeness and knowledge of what sells in its region. Suppliers also have to understand the impact of national trends on large retailers like Wal-Mart and be prepared to adapt. The key to impressing a powerful buyer is to display an understanding of the potential market.