The next time a cashier asks you if you'd like to save 10% instantly just by applying for a shiny new piece of plastic with the store's name on it, think twice before saying yes. The real motive might just be to pad her own paycheck instead of saving you a little coin.

Everything might not be better

Their TV ads feature the late Bob Hope in a Santa hat saying "Everything's better at Macy's..." But "better" might not be "best" for your holiday budget.

When she worked as a manager at Macy's, Jennifer Krosche was offered some great employee incentives. " Macy's would pay employees $5 in Macy's money, which we could only use in the store, for every new Macy's charge card application we'd get," says Krosche, explaining that the store would run promotions by which employees could net bonuses. "Other times, it was $5 in "Macy's Bucks" for every three to five new accounts."

Macy's isn't the only retailer urging employees to sign us up. Krosche, who also worked at Banana Republic, says employees there had a monthly goal of opening five new cards a month. "Any less, and you'd get a tutorial on how to open cards and a "conversation" about why you weren't." She says the employee who opened the most cards every month won a prize. "As a manager there, I was always coming up with incentives for employees to open new credit cards."

What's it to them?

Retailers push to add more plastic to your wallet solely to boost their bottom line. "It's all about profit," says Jim Randel, author of The Skinny on Credit Cards. He says stores are usually happy to slash 10 or 15% off the price of purchases since they can make two, three or five times that on the interest you'll be charged paying off the card's balance.

"Unless you pay the balance off in full as soon as the bill comes, those instant savings "deals" are often no deal at all." Randall says.

Retail or "branded" cards usually carry a high interest rate, or jump up to a high rate after the promotional period expires. If you carry a balance, the instant savings will be negated by the interest you'll pay back on the purchase. For instance, Randall says, if you receive 10% off a $100 purchase, that creates a "sale" price of $90 (plus tax). "If you make a minimum payment [in this case, $10 to $15], that "sale" purchase will cost you about $107 -- $7 more than if you paid in full at the register and never opened the card in the first place.

Assessing the savings

This holiday season, before accepting the cashier's offer, ask yourself just one question. Do I have the money to pay this new charge off in full with the first statement?

If not, don't open the card. It's as simple as that. You'll most likely end up spending more in interest that you'll save at the register.

Sound off. Do you think employees should be pressured to open new customer credit accounts? Are you tempted to open a new credit card to save instantly at the register?

Gina Roberts-Grey is a freelance writer specializing in consumer interest issues.