More than that. They have your frequent shopper card and your online purchase history and everything else they've aggregated together. They know at what prices you purchase things, they know how much you shop around, they know the days of the week and times of day your more likely to make an impulse purchase. It's lunch on Tuesday and your favorite snack suddenly costs five cents more because they're moving the Overton window on your price points. It's after work Friday and suddenly everything costs 10% more because they know it's the end of the week and you're tired and aren't going to go to another store.