Do you use credit cards frequently when you shop for the convenience or rewards? Are you also a bargain hunter? If so, using your credit card might not be the best idea. While your credit card can make it convenient for you to make a purchase when you spot an unbeatable deal, it can also counteract any savings you expect.

Here are three ways credit cards can sometimes turn great prices into bad deals.

1. Interest payments are greater than savings.

Let’s say you want to buy some new furniture for your home. You come across a great short-term sale on a furniture set you like. You can’t afford to pay for it all up front, so you put it on your credit card.

If you can pay off this purchase reasonably fast, you might be able to avoid interest or at least keep interest payments low. But if you need several months (or even years) to pay off the balance, make sure you find out how much the interest charges will cost you when compared to the up front savings during the sale.

2. It’s only a good deal if you really want or need something.

No matter how much money you might save on something, it isn’t really “saving” if it’s something you don’t want or need in the first place. That’s one problem with credit cards. They can make it too convenient to make impulse buys. If you’re going to a store where you tend to feel tempted, consider bringing a limited amount of cash instead. You’ll have to put more thought into purchases, and that goes beyond what you see on a sale sign.

3. Convenience can override comparison shopping.

The same convenience that can lead to credit card impulse buys can also defeat your goal to save by letting you rush to buy things. Let’s say you visited a store and saw an item you planned to buy soon anyway. It’s on sale for 20% off the regular price. It’s the last day of the sale. So you pull out your credit card and make the purchase.

If you were really serious about finding bargains, you wouldn’t rush to buy it in the first store where you saw it. You would comparison shop first. Maybe that 20% deal really was the best offer around. Or maybe the store down the street is selling it for a 25% discount.

That’s not to say that you have to get the absolute best deal on every purchase you make using your credit card. If you’re happy with the savings you received and interest doesn’t cut into those savings too much, you still found a decent deal. There is value in convenience for all consumers at different levels (such as whether you’d rather visit a second store or save time with the smaller discount). That’s up to you. But knowing the ways credit cards can impact otherwise attractive deals is an important part of being an educated consumer.