I recently learned that most marital cheating occurs at the checkout line at Ralphs. Frankly, this came as a surprise because I find the lighting at Whole Foods much more forgiving and I have heard the Muzak version of Marvin Gaye’s “Sexual Healing” more than once while shopping at Vons. But according to my sources, it is Ralphs where most (but not all) of the local cheating occurs. Amazingly, the trysts take place in the checkout line in plain sight of anyone who is paying attention.

The typical scenario plays out like this. Wife, tired of hearing her husband decry every category on the family credit card bill except for groceries, purchases gift cards to local department stores or generic pre-loaded MasterCard or Visa cards at the supermarket checkout line. Do you see where this is going? The unsuspecting husband scans the monthly credit card bill and sees biweekly charges for “Ralphs,” never suspecting that anything besides groceries was purchased. Wife gets to buy the shoes she had her eyes on at Nordstrom without having to justify the purchase to her spouse. OK, so it is not Gen. Petraeus-level cheating, but isn’t it cheating, nonetheless?

When I first heard that “everyone” knows about this supposedly ubiquitous gift-card scam, I should have been horrified. After all, there is not a ketubah out there that reads: “You are my husband according to the tradition of Moses and Israel. I shall cherish you and honor you as is customary among the daughters of Israel who have cherished and honored their husbands in faithfulness and in integrity except when at the supermarket.” Instead, my reaction was more of a combination of empathy mixed with admiration for the ingenuity. As a woman who has had to defend the expenses on a credit card bill to her husband more than once, I related. The process of justifying your purchases is exhausting, humiliating and often perplexing. (How the heck did the credit card bill get that high?)

Apparently I am hardly alone in this situation. It seems that no matter how much or how little money a couple has, lying about a purchase is rampant. According to a study commissioned by SmartMoney and Redbook magazine investigating how couples handle money issues, 36 percent of men and 40 percent of women admitted that they had lied to their spouse about something they had purchased. And while none of my close friends have fessed up to participating in the gift-card scam, nearly all of them complain about a marital dynamic where their spouses frequently criticize their spending but are defensive about their own big-ticket purchases. Whether the wife works outside of the home or not, the interaction seems to be the same: husband on the offensive, wife on the defensive. (Although, interestingly, my own parents were the exception: My mother was the major saver, and my father was the big spender.)

The SmartMoney survey concluded that differences over how the marital money should be spent are the second-most-common reason why couples fight. According to Ruth Hayden, author of “For Richer, Not Poorer: The Money Book for Couples,” the problem is that “one spouse gets labeled the ‘spender’ and is blamed for skimming all the money out of the checkbook. In most cases, however, that’s not accurate.”

“Studies show that men and women spend the same, they just spend differently,” she says. Women usually take care of most of the family’s daily expenses: the groceries, the bills, clothes for the family, while men spend on large purchases like plasma TVs, cars or computers. “If you counted up your money, you would be spending about the same,” Hayden says. “But because you spend so differently, the perception is different.”

Of course, the notion that disagreements over money frequently cause a love deficit did not come as a surprise to me. As someone who has practiced family law and wrote a book on the causes of divorce — not to mention been married for nearly two decades — I am all too familiar with the long-term damage these fights over short-term spending cause. Money disputes are an equal opportunity marriage destroyer affecting both the rich and those struggling financially. As one attorney I interviewed for “The Divorce Lawyers’ Guide to Staying Married” put it: “The amount of money a couple has doesn’t change the basic reasons that people get divorced. Whether the family income is $75,000 a year or $750,000 doesn’t make a difference. It is all about the way the couple relates to money.”

Like most issues that cause marital strife, there is no simplistic “Modern Family”-esque ending where the players argue and shout, but then miraculously have a love-conquers-all epiphany in the final two minutes. The truth is that the role money plays in a marriage is extremely complex. It brings out differences in values, raises control issues, touches on entrenched feelings about gender roles and highlights differences in spenders and savers. And because most of our attitudes about money are etched into us during our childhoods, they are extremely difficult to change. So what’s a frustrated married couple to do?

The short answer would be to seek help in the form of a marriage counselor or financial adviser. But what seems to work for most is being able to make independent decisions over certain expenditures without oversight by the other partner. For this to work, both spouses need to have access to a reasonable amount of money that they can spend (or save) without question or comment. It needs to be enough so that she doesn’t feel the need to throw in a couple of gift cards between the milk and bread on the supermarket conveyor belt and he doesn’t feel compelled to buy the new BMW as payback for bulging credit card bills. But it can’t be so much that the loss of that money will create irreparable resentment or financial ruin.

Is this solution perfect? No, but as this former divorce attorney knows, it sure beats the alternative. Yes, there is a difference between slipping your e-mail address to the cute man/woman standing in front of you in the checkout line and slipping an $100 “shoe” gift card to the clerk. But it is a difference that is measurable in inches … not in “feet.”