When shopping, we behave differently when we pay in cash versus when we use a card (credit, debit, or gift). This is one of those everyday anomalies that belie our economic rationality, and many theoretical expectations, and yet that make sense. The feel of having cash in hand, the deliberate act of handing over bills, the material loss of paying--the very physicality of the act focuses our attention sharply on price. Using a card is "one step removed from having green cash money leave [your] flesh-and-blood hands," and thus the pain of paying is made more distant, as Ron Lieber argues in the NY Times.
Studies have shown that customers are willing to pay significantly more for the same item when using a card, and that card paying consumers are more concerned with features and quality compared to price. Thus, Dave Ramsey and a host of self-help gurus advise us to use cash as a way of nudging us to be more rational and prudent. Paul Roberts argues in The Impulse Society that credit cards feed into our accelerating desires for instant gratification.
But perhaps there is an upside to being less price sensitive (within reason, of course). In my book The Good Life, I look at German shoppers, who still mostly use cash in their supermarket transactions. They often express a preference for products that carry positive social values (organic, fair trade, etc.) and for quality. Yet, when the cash actually changes hands, they often opt for lower priced alternatives. This suggests that paying in cash curbs our enthusiasm for doing the right thing. Perhaps, then, when one can afford it (a separate issue), we would be doing more for the greater good to be less price sensitive--willing to pay for quality and the job dignity and social values that go with it.