1. If every aisle smells like freshly brewed coffee or just-baked cookies, the store might be using scent to activate your brain's caving-and-reward center (the same place that makes you want popcorn as soon as you hit the movie theater). Once that desire is awakened, you're much likelier to buy more, says Melissa Hobley of the branding research company Buyology Inc.
2. When you catch yourself dancing in the aisles to the rockingest version ever of "Deck the Halls," you may want to head for the checkout lane: A recent study showed that about 70 percent of retailers believe music will make you lose track of the time you've spent shopping--and the longer you're in the store, the more you're likely to spend.
3. Does the cart suddenly look as big as Santa's sleigh? Some stores have supersized their carts, possibly flirting with your hunter-gatherer impulse to stock up, according to findings in the Harvard Business Review. So fight the urge and stick to your list--but if that's also the size of a sleigh, don't sweat the size of your cart!
4. Don't discount your inbox! Online retailers have done studies on the time of day you're least likely to resist those "limited time offer" and "flash sale!" alerts, Hobley says. (Beware of shopping after lunch.) So whenever you find yourself sitting at your desk thinking, "If I don't get this now, I'll miss out," wait a beat before you purchase. On the other hand, this is the holiday season. Live a little!