A credit card, on the other hand, sets up a charge which is added to all of your other charges for that month by the issuing bank and sent to you at the end of the month in one bill. When you write a check to pay the bill, only then is money deducted from your checking account. If you do not pay the entire bill, you are charged interest on the unpaid balance.

The advantage of debit cards is that they will never get you into problems with overcharging (if there is no money in your account, you can't use the card). But the disadvantage is that they do not offer you as much protection as a credit card.

If you buy something with a credit card, the law gives you certain protections. In effect, the credit card company is required to act as intermediary for you with the vendor should problems arise. Look at the back of your credit card statement. The fine print explains the obligations of the credit card company.

If you write (calling does not qualify) to the address they give you within 60 days of noticing a charge you wish to dispute on your credit card bill the credit card company must investigate your question and respond in writing. To make this easier for you, the credit card company may supply a simple form right on the bill which you can fill out and send in.

Common problems that might cause you to write are: The item was not as advertised, you were double billed, they failed to deliver the item, returned items were not credited, and the wrong amount was billed. The credit card company will look into any of these and try to get the merchant to straighten out the problem. If the merchant does not answer them in a timely fashion, the credit card company may remove the item from your bill until they get a satisfactory answer.

In any case, while they investigate your claim, you are not required to pay the amount in question. They cannot charge you late fees for not paying it. And they cannot charge you interest on the amount. It will stay on your bill, but it goes into limbo until they have investigated and responded.

None of these protections are available when you use a debit card. So I recommend that if you want to use a debit card, restrict your use to items you purchase in stores and take with you — items with which you are unlikely to have a problem.

Paul Schrader is Executive Director of the Cape Cod Consumer Assistance Council (CAC) , one of 19 local consumer programs in Massachusetts sponsored by the Attorney General's Office. Relying heavily on volunteers, these organizations attempt to mediate consumer problems with vendors. There is no charge for the service. If you have a problem with a vendor, call the CAC at 508-771-0700.