In Why We Buy: The Science of Shopping, Paco Underhill describes a variety of methods retailers use to enhance sales. Some of these are obvious, such as placing sweetened cereal at a kid-friendly height, or surrounding the checkstand with cheap impulse items. But other techniques are more subtle. Fortunately, knowing what's likely to make you buy can actually help you to avoid being suckered. Want to win the retail battle? Here are some easy changes you can make to reduce your spending.