The online version of the Telegraph has an article on how psychology is used in shops to persuade us to part with our hard earned cash and lists some common tricks and techniques.
“The most important rule as a shopper is to keep your wits about you,” Karl says. “If you enter a retailer’s property, in one sense, you lay yourself open to any tricks or techniques that they might want to spring on you. The best armoury you can have is to keep your eyes open and your ear to the ground and see what’s going on.”
Link to article (via metafilter.com).
Mind Hacks 
Ah…But how to keep your wits about you! This is, i think, where the psychology of marketing and possibilities for individual freedom intersect – no trick used by marketers is coercive, neither are they usually very smart. I know that aftershave adverisers, say, are just trying to make me associate their product with an astonishing success with members of the opposite sex – and if i’m really thinking about this I can see it for as laughable a proposition as it really is.
But the point is: who has time to think, all the time, about every single consumption choice they make? Answer: no one. We don’t have the mental resources, or time, to ‘keep our eyes open’ to every trick the advertisers pull. Especially in situations, like supermarkerts, where we are in a hurry, often harrassed and with a limited set of priorities (eg “buy dinner”, “get home in time for 8”).
Individually, given time, we may all be fairly rational decision-makers, but aggregate us into a time-pressed, distracted, crowd and there’s easily enough collective irrationality to keep the advertisers well-funded.