We're just days away from Jan. 1, and you know what that means -- awesome New Year's sales!

If you haven't already been assaulted by year-end, "December blowout bonanza," "you won't believe these prices" marketing materials, just wait. Resistance is futile.

Crafty marketing geniuses know exactly what buttons to push to get us to hand over that last wadded-up dollar bill in our coat pocket. We can't help but supersize our fries and load up our grocery cart with sale cheese products in a can. It's human nature to get more when the getting's good -- or at least when it seems to be. Price tags that have the words "Buy Now" or day-old sourdough loaves on sale for "2 for $5!" (when just one loaf at $2.50 and no exclamation point would do) work wonders on our spending psyche.

In Influence: Science and Practice, a book on the science of selling, Arizona State University psychology professor Robert Cialdini examines the "triggers" that make us buy strawberries in bulk and dreadful sweaters that we never wear. Should you find yourself drifting within retailers' zone of influence in the coming days, brace yourself for these scientifically proven selling tactics:

Reciprocity: When a stranger sits by us at a conference and offers his extra can of soda, we're much more likely to agree to visit his booth afterward to hear his company's sales pitch. There's no surer way to lose all your money than falling for a pretty face pushing penny stocks. As Selena Maranjian writes, it's the fastest way to "get stupid quickly." Buy your own soda, and kindly excuse yourself from the sales schtick.

Consistency: When we get a fabulous haircut at a chichi salon, we're more apt to buy expensive hair products because it's consistent with the "persona" of someone who would go to that salon. Look at the bottles, and tell the receptionist you already have what you need at home. She doesn't have to know you're using dishwashing liquid with Scrubbing Bubbles on your scalp.

Likability:Tupperware (NYSE:TUP) and Avon (NYSE:AVP) parties work because they get someone who presumably likes you to put you in a buying situation. And no one wants to be the deadbeat friend who refused to buy the 32-piece Keep 'N Heat Serving Set. Even if we're single and have three cups to our name. Come with hors d'oeuvres, and leave your checkbook at home.

Authority: The college student standing behind the EsteeLauder (NYSE:EL)-owned Clinique counter in her white lab coat must know more than we do about the benefits of the $42 antioxidant neck cream. Remember -- she was hired because of her youthful, firm neck, not her science smarts.

Scarcity: The makers of Beanie Babies had it right when they made limited quantities of these furry friends. Consumer desire skyrocketed for a beanbag toy. (See also: Cabbage Patch Kids.) Look around you, and see whether you can pick out any item in your possession that you could not live without -- or live with a different brand.

Social validation: "You listen to Kenny G? Me too!" This technique has been adopted quite successfully by singles in bars looking for a match made in heaven. Don't bother blowing a fortune on anything designed to project an image of someone you are not. And by the way, Kenny G never makes you seem cool.

If you recognize these ploys, Cialdini says, you can brace yourself for the onslaught of buying triggers.

More shopping tips that will save you thousands!

Dayana Yochim owns none of the companies mentioned in this article but has fallen for sales pitches from all of them. The Fool's disclosure policy is followed by all the cool kids.