By Aaron Crowe

I went to Sears recently to buy a pair of shoes for my daughter, not knowing that paying for them would turn into a math lesson for the entire family.

I paid for the $20 shoes (on sale from the original price of $30) with a credit card, and was told by the cashier that the price would drop to $6 if I opened a Sears credit card on the spot. I'm usually happy to get 70 percent off, but I declined for a few reasons -- the main one being that I wanted to get out of the store quickly after finding the shoes.

I also didn't want to get stuck with a store credit card that would be another thing to keep track of and pay off each month, even if the initial deal was as eye-popping as it was. Store-branded credit cards, I've learned, are things to be wary of. Many of them.

Limitations of store credit cards

For starters, I can only use the store credit card at that store. We had a Kohl's store credit card a year or so ago, and it offered all sorts of discounts for the constant and confusing sales Kohl's is known for. It also charged a hefty late fee when we didn't make a payment in time, and going to the store to pay it wasn't a fun outing. I don't remember what the charge card's interest rate was, but I remember it was more than we pay with our regular credit card -- which is accepted by most stores.

Department store credit cards are often pushed at the cash register -- not a place to make such an important financial decision and definitely not a credit move to make on an impulse. Who wants to be bothered with such forms with a line of shoppers lined up behind them?

I also like to comparison shop when I can -- usually online -- so having a credit card that can be used everywhere makes more sense than being tied to one store with its card. However, if we were buying thousands of dollars in furniture and appliances in one trip, the Sears card discount would be worthwhile. And then I'd cancel the card after paying it off.

These cards are financed through the store company itself, and shouldn't be confused with co-branded cards that are usually backed by a major bank -- although these are another type of store credit card to avoid unless you shop there a lot.

Review: Toys"R"Us rewards card

Toys "R" Us teamed up with Chase for its new branded rewards credit card as a way to attract more loyal shoppers to the "R" Us brand this summer.

The Toys"R"Us & Babies"R"Us MasterCard from Chase gives more reward points (four per dollar spent) for things bought at Toys "R" Us and Babies "R" Us than at other stores (one point per dollar spent). That's typical of such cards, which could be a good deal in this case if you're buying a lot of toys and baby gear every year.

The Toys"R"Us card also gives a certificate for $10 off for every 1,000 points earned, up to three per month. In other words, if you spend $750 a month for toys and baby supplies there, you can get 3,000 points, which converts to $30 off future purchases. Big deal.

But even if you do shop at Toys"R"Us a lot, and the credit card can be used at other stores, the store's card may not be the best deal out there.

You may be better off with a rewards credit card that gives you more than 1 percent back on all purchases, or at least a better payback on something you're more likely to use often.

That new barbecue grill and lawn furniture set is looking tempting at Sears, but I still don't think I'll be going for the store's credit card discount.