In this economy a lot of people are on tight budgets, so an unexpected hold on the money in your checking account can really hurt.
There's an estimated 530-million debit cards in use in the US. Some merchants who accept them use a little trick to protect themselves, but by doing so they could put you in a financial pinch.
Pre-authorizing a higher amount on your debit card is a common and perfectly legal practice among certain types of merchants - typically gas stations, rental car agencies, and hotels.
It's common for a gas stations to hold a set amount when you purchase gas, since they don't know how much it takes to fill your tank. They may put a hold on $75 when you may only purchase $10 worth of gas.
Hotels often get pre-authorization on an extra amount above the nightly room rate to cover incidentals like mini-bar purchases, movie rentals, phone calls and room service.
Those holds that protect the merchant can linger on after the point of sale. It freezes the entire pre-authorized amount, no matter how much the bill actually is. There are some time limitations though. They have a maximum of 72 hours to complete the transaction.
The problem is merchants don't have to tell you how much they're going to have held, so buyer beware.
The Consumer Credit Counseling Service suggest asking the gas station, hotel or car rental agency if they put a hold on additional funds. If they do, make sure you know how much so you can factor that into your budget, or pay with cash or a credit card.