If there's one thing that drives this coupon-user crazy, it's going home only to realize that a coupon I used didn't work properly. While that can happen on occasion at any store, Target has admitted that some manufacturers coupons have been ringing up improperly for months, blaming a computer glitch that the Minneapolis-based retailer says it is working to fix. In the meantime, Target said cashiers should be checking coupons for problems.

As for shoppers? We should always pay close attention at the prices that ring up at the registers whether a problem has been identified or not. But smart coupon use goes beyond having a watchful eye. Consumers commit coupon mistakes in checkout lines all the time. Are you guilty of a common coupon oops?

Mistake: You think purchases with coupons are always the best deal. "You shouldn't be tempted to use a coupon just because you have it," said Annette Economides, who runs the website www.americascheapestfamily.com with her husband Steve Economides. The couple recently wrote a book about saving money on groceries. "The bottom line is how little cash can we pull from our pocket and still eat well," she said. But some people feel an irrational pressure to use their coupons even if a store brand is cheaper, or they never would have purchased that bag of chips without one in the first place. Steve Economides says to think of coupons as an ad. "They're marketing the product to you promising a deal and if you're not savvy about your prices, you could actually overpay," he said. Not only that, but manufacturers love to introduce new products with high-value coupons. But don't be surprised when the coupons stop once your family is hooked.

Mistake: You use a coupon right away or don't hold onto it long enough. Consumers are sometimes surprised when Carrie Rocha, founder of www.pocketyourdollars.com, tells them that it's not just produce that has seasons. Packaged goods and coupons promoting them have seasons, too. "When a product is in its peak season, it goes on sale more frequently and at lower prices ... that's the time that a manufacturer releases more and higher-value coupons for that product," she explains. For example, manufacturers are unlikely to release their highest-value coupons for summer items such as razors, barbecue sauce and baked beans in November. Look for frozen vegetable, canned soup, cold medicine and baking supply deals going into winter. The wisest shoppers know to wait and use a coupon when an item is in season and on sale and then stock up.

Mistake: You fail to ask. Maybe the item you could get for free with coupons has been wiped off the shelf by other deal seekers. Don't leave the store without asking someone to check the stockroom, or without requesting a raincheck. Perhaps the high-value coupon you were waiting to use expired yesterday or a coupon you know is legitimate is being refused by a cashier. Talk to a store manager. I'd weigh the value of your coupon against the time these strategies take, but for a high-value item, it's probably worth the hassle.

Mistake: You toss expired coupons. Rocha said some stores will take expired coupons at the manager's discretion, especially if the store is very close to another grocery store or big box. Cub Foods, for example, takes expired coupons for three months. Ask your local store's manager about the store-specific policies regarding expired coupons, price matching and Internet coupons. Familiarize yourself with a retailer's corporate coupon policy. That is, if you can find it -- many policies either aren't posted on the corporate website or are impossible to locate.

Mistake: You fail to read the fine print. "Pay attention to the wording on the coupon," said Christina Brown of Bovey, Minn., who writes the money-saving blog www.northerncheapskate.com. Sometimes coupons don't have size exclusions, meaning you can get the smallest size for free. Other times, the fine print reveals that several items work with the coupon, not just the premium-priced item pictured on the coupon.

Mistake: You only clip coupons from your Sunday paper. Your newspaper is still a great place to start, but it's the 21st century. Head online. Most cashiers no longer look at you funny when you hand over a wad of printed coupons. Fan a favorite brand on Facebook. Visit a coupon site such as Rocha's www.pocketyourdollars.com that will link you to online coupons. Sign up for e-mails on a manufacturer's website. Check out a store's website before you shop. You do need to feel comfortable trading some personal information with retailers for discounts, but if you're OK with that, you can multiply your savings.

Kara McGuire • 612-673-7293 or kmcguire@startribune.com.