Dude... if your bank charges you ATM fees for POS transactions using your debit card, you need to change banks.
Part of the problem at gas stations may be the way they handle credit cards; when you swipe the card, they put a "hold" on the account for the price of an average tank of gas (this is before they know how much you're going to actually spend), in an attempt to guarantee you have enough money to pay for whatever you get. Then when you're finished, they send a message to cancel the hold and charge you x amount of money. If you don't have enough money on your card for whatever they've decided the "average" tank of gas costs, it'll get declined. Plus it can take longer for the 'cancel' order to go thru than the charge, so if you've done a lot of shopping in establishments that do this, it will seem to the machine that your card is overdrawn when it isn't. Debit transactions ask the bank's computer what your balance is before letting you buy (which is why if you want to buy $20 and your balance is only $15, some pumps will turn off at $14 and tell you no).
(no subject)
Part of the problem at gas stations may be the way they handle credit cards; when you swipe the card, they put a "hold" on the account for the price of an average tank of gas (this is before they know how much you're going to actually spend), in an attempt to guarantee you have enough money to pay for whatever you get. Then when you're finished, they send a message to cancel the hold and charge you x amount of money. If you don't have enough money on your card for whatever they've decided the "average" tank of gas costs, it'll get declined. Plus it can take longer for the 'cancel' order to go thru than the charge, so if you've done a lot of shopping in establishments that do this, it will seem to the machine that your card is overdrawn when it isn't.
Debit transactions ask the bank's computer what your balance is before letting you buy (which is why if you want to buy $20 and your balance is only $15, some pumps will turn off at $14 and tell you no).