Credit cards can be a real convenience, but they can also be really bad news. It all depends on whether you work for the credit card, or whether you make the card work for you.

Some new information compiled today by the Government Accountability Office (the nonpartisan folks who do research for Congress) shows that some consumers have taken advantage of competition among cards to reduce their interest rates.

Back in the last century, even before the Internet, virtually all credit cards came with a fixed 20% interest rate. In the '90s, when credit cards started falling from trees, interest rates started to come down. As of last year, 80% of cardholders had interest rates below 20%, and about 40% had interest rates below 15%.

Many credit card users prove themselves downright responsible. Half paid their entire balance each month last year. Only about one-third were charged a fee for late payment.

That's good news and bad news. The flipside of those statistics shows that some cardholders could clean up their acts a little.

Two out of 10 of cardholders pay interest rates greater than 20%. Those sky-high rates often result from what lenders call the default rate. That's the rate card companies can charge if they detect behavior, like late payments, that they believe shows you're a risky borrower. The government researchers found the default rate among the biggest credit card companies averaged 27.3%!

The Foolish Credit Center recommends that cardholders try to negotiate interest rates of 12% or lower. We can give you tips for calling the card issuer and asking for a lower rate. Otherwise, check the mailbox for one of the million balance-transfer offers you've probably received today. (Read the fine print before agreeing to anything.)

Many cardholders being charged interest rates between 15% and 20% could make those calls, too, and join the rest of the credit users who have made the competition for credit card customers work for them.

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Fool contributor Mary Dalrymple welcomes your feedback, but not your credit card debt.