Many stores have an in-store credit card that is offered to you at the register, usually with some intriguing pledge like taking 10% off your current purchase. While it's tempting, it's not worth signing up for many reasons.
First, the interest rates on in-store cards are often incredibly high, some approaching 30% annually. That means for every $100 you leave on the card, they charge you $30 a year for that service.
Second, the card itself tempts you to go back to the store, as it has the store's logo loudly branded on it. When you see it in your wallet, you'll be tempted to go back and shop using the store credit card and accrue more interest if not paid off promptly.
Third, every time you open a new credit card, you not only get a small negative impact on your credit report (especially if you miss a payment), but you also slightly increase your chances of identity theft. Add them up and a store credit card simply isn't worth the $10 or $20 you might save in the moment.
Credit: 365 Ways to Live Cheap