Other retailers find it offensive on its face that they should have to offer a discount to people who use United States legal tender. How, they ask, did we come to a point where anyone would even be bold enough to suggest something so outrageous? Besides, it makes little sense to hand over money to people who are already paying cash without knowing how many card users will join them, if any.

Then, there are the rules in some states that require retailers to display both the cash and credit price on every single item. That might work for a gas station but be expensive for a big-box retailer.

John Rydman, co-owner of the Spec’s chain of wine and liquor stores in Texas, offers a 5 percent discount to customers who use cash or punch in their PINs when using their debit cards. He decided to mark every item in the store with two prices, even though the state didn’t require it. “We do it for the ease of the customer, because they can’t do the math generally,” he said.

You’d think his largess would satisfy every customer, but it does not. “Some people don’t get it and don’t like it,” he said. “They’re mad that nobody else does this to them.”

Indeed, this is the problem that gas stations can face, according to Jeff Lenard, a spokesman for NACS, an industry group that represents convenience stores and gas stations. If they introduce a cash discount, many card-using customers will drive on by, assuming that the station owner has in reality simply raised prices for people swiping plastic. If the station owner then capitulates and establishes a single price again, cash customers who were getting a deal before now think prices have gone up again, and they, too, find another place to fuel up.

Life might be simpler and more efficient if retailers could levy a surcharge that covers their costs to accept cards and let consumers figure out whether to pay it. But the card companies don’t allow that, and Congress hasn’t yet forced their hand, though this is now how things work in Australia (where some retailers charge excessive fees, alas).

So what’s an American consumer to do in the meantime? For help answering that, I turned to Dave Hanson. Mr. Hanson, a Spokane, Wash., resident, is one of the savviest card users I know. He also happens to have studied philosophy in graduate school at the University of Chicago and taught applied ethics at Gonzaga University.