Once you enter, there's the shopping cart. This invention was designed in the late 1930s to help customers make larger purchases more easily.
Source: Idea Finder
In supermarkets, high margin departments like floral and fresh baked goods are placed near the front door, so you encounter them when your cart is empty and your spirits are high.
Flowers and baked goods also sit near the front of stores because their appealing smell activates your salivary glands, making you more likely to purchase on impulse.
Supermarkets like to hide dairy products and other essentials on the back wall, forcing you to go through the whole store to reach them.
Once customers start walking through a store's maze of aisles, they are conditioned to walk up and down each one without deviating.
Source: Levy and Weitz 1997. Read more here.
Most stores move customers from right to left. This, combined with the fact that America drives on the right, makes people more likely to purchase items on the right-hand side of the aisle.
Source: AllSands
Anything a store really wants customers to buy is placed at eye level. Particularly favored items are highlighted at the ends of aisles.
There's also kid eye level. This is where stores place toys, games, sugary cereal, candy, and other items a kid will see and beg his parents to buy.
Stores also want items to be in easy reach. Research shows that touching items increases the chance of a purchase.
Source: lifehacker
Color affects shoppers, too. People are drawn into stores by warm hues like reds, oranges, and yellows, but once inside cool colors like blues and greens encourage them to spend more.
Source: ?Bellizzi et al. (1983). Full citation here.
Hear that music? Studies show that slow music makes people shop leisurely and spend more. Loud music hurries them through the store and doesn't affect sales. Classical music encourages more expensive purchases.
Cain-Smith & Curnow (1966); Milliman (1982 & 1986); Caldwell & Hibbert (1999); Areni & Kim (1993). Full citation here.
Store size matters, too. In crowded places, people spend less time shopping, make fewer purchases (planned and impulsive), and feel less comfortable?.
Source: Harrell & Hunt (1976); Gillis et al. (1986). Full citation here.