Woman shopping at a store © Jack Hollingsworth, Brand X, Getty Images

The list of questions you get asked at the checkout counter seems to grow every year. In addition to the standard, "Did you find everything you're looking for?" inquiry, customers may also be asked to donate to charity and to hand over an email address for store newsletters. Another common question: "Would you like to sign up for our store credit card?" -- to which millions of Americans each year say yes. According to a recent report by Equifax, more than 175 million retail credit card accounts are open nationwide, a 31-month high.

Such cards are usually packed with perks. Signing up might mean a big discount on whatever you're buying; the store card may also provide you with discounts on future purchases. But like other credit cards, these retailer-branded cards often have terms that can get you in trouble if you don't understand them fully. Here’s what to look out for if you're thinking of signing up for one of these cards:

Consider the rate

As with any credit card offer, the interest rate is the most important number. That's especially true of store-brand cards, which can carry high rates.

"If you're a cardholder that tends to carry a balance, then you should be looking at the rate," says Ruth Susswein, deputy director of national priorities with Consumer Action, a consumer advocacy nonprofit. "Generally, the rate tends to be a good bit higher. And if you're someone who's going to be paying the balance off over time, that matters."

Credit.com personal finance expert Gerri Detweiler agrees that you're likely to find the interest rate to be higher than what you'd get on a standard credit card from your bank.

"Every retailer card will fail the test if you compare the rate to what you could get with a regular credit card," she says.

Susswein also points out that applying for a new credit card account will ding your credit scores, especially if it's possible that you'll be denied. If you think there's any danger of denial, or if you're going to be taking out a mortgage in the near future, you're probably better off passing.

Consider the perks

If store credit cards have higher interest rates than average cards and could lower your credit scores, why would you sign up for one?

The perks, of course.

The rate, and the kind of interest payments you're likely to make if you carry a balance, should be weighed against the deal being offered by the retailer. A significant discount for opening the card, plus a recurring discount every time you use it at the store might make it worth it getting.

"If this is a place you shop regularly, it could be a way to get a regular discount," Susswein says. If the store card gives you 5% off at that retailer every time you use it, that's better than the 1% to 2% cash back you'll get from a typical rewards card.

The more lucrative benefit, however, is likely to be the discount you get at the point of sale. With such percentage-off deals, the bigger your purchase, the bigger the benefit.

"If you're buying $100 of merchandise at a department store, that would not be enough to motivate me to open a new store card, but if you're buying $5,000 worth of appliances, it's a different story," says Detweiler.

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Understand 0% financing terms

One common deal attached to these credit cards is an offer of 0% interest for an initial period, provided you use your card to buy a certain amount of merchandise for that period -- for instance, putting $500 on the card within the first six months.

There are a few things to look out for with one of these deals. The most obvious is that you don't want to put yourself in a position of needing to buy merchandise you don't need just so you can put off paying interest. And you should also make sure you establish whether you need to make minimum monthly payments during that time.

More important, though, is that the balance may be accruing interest in the background during that six-month period.

"You won't have to pay any interest if you pay off the purchase in full in the period," says Kathleen Day, a spokeswoman for the Center for Responsible Lending. "They're just hoping you'll forget, at which point you have to pay all the interest (you've accrued)." 

If you play your cards right, it’s essentially an interest-free loan. Take the Home Depot card, for instance, which charges no interest if you spend at least $299 in a six-month period and pay it off in full.

But as the card's terms make clear, if you goof and let the interest-free period expire without paying up (or if you miss a minimum payment), you'll suddenly get hit with six months' worth of interest. And as Day notes, the interest rate on that balance is often higher than what you'd pay on your normal credit card.

Make sure it's a credit card

Not all retailer cards are of the credit variety. Sometimes they're actually debit cards, and that means a whole different set of conditions in thefine print to pore over.

Take the case of Jamie, whose story was told at Credit.com. Jamie took out a Target-brand debit card, which was linked to a checking account and offered 5% cash back when used at the retail chain. Unfortunately, she didn't realize that the cardholder agreement automatically signed her up for overdraft protection, and when she used it without enough money in the bank, she wound up with a $30 insufficient funds fee.

Because the card was issued by a retailer rather than by a bank, federal laws didn't prohibit Target from automatically signing her up for the service. The lesson? Whether the store is issuing you a debit or credit card, read the cardholder agreement carefully.

Of course, that's not always easy to do when you have impatient shoppers waiting in line behind you at the store, which is why Detweiler says she isn't crazy about signing up for cards at the point of sale.

"I'm not a fan of opening store cards on the spot, because it just doesn't give you time to think through terms of the card," she says.

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