If it was Dollar General then you're fine. The full process on PIN transactions is
- Swipe, insert or tap your debit card
- Enter your PIN
- Store withdraws whatever your total is from your account (there's a bit more to this but it's not relevant here)
The credit process on a debit card is slightly different
- Swipe, insert or tap your debit card
- Store authorizes the total amount (this is how all credit transaction work, debit or not)
- Your bank withdraws the authorized amount from your account
- At the end of the day, the store runs what it called a settlement. That tells their merchant service to capture the money. Since the full amount of the transaction has already left your account, you're none the wiser
If the amount is low enough, most stores have an agreement that you don't need to sign for it (hence the clerk swiping and telling you you're "good to go").
There's two places where that debit-as-credit process can trip you up, however
Gas station pay-at-pump credit
Virtually all pumps run an authorization of some low amount (in the US, this is typically $1). The gas station then captures the full amount at the end of the day. This can be problematic for you if you don't remember the full balance of your transaction.
Let's say it's Friday night and you buy $50 in gas, having run it as credit at the pump. You check your bank balance on your phone and see you have $200 showing as a balance. You spend $180 over the weekend. The problem is that the pump only authorized $1, so come the next business day (typically Monday), the merchant account of the gas station is going to have captured $50. Your bank will process that the same or next day (depending on how they do things) and try to debit $49 from your account, but you only have $20 left now. This typically carries an overdraft fee.
Online transactions
A slightly different problem exists online. It's gotten less common now, but it's still out there. By definition, you only run online orders as credit. Most of the time that's not a problem, but if your payment failed, it could cause issues.
Some merchant accounts will try to authorize the full amount of your transaction as a way to ensure there are sufficient funds. This typically happens after they verify your CVV2 number (3 or 4 digit number printed only on the card, separate from the card number) and zip code (address verification). Some merchant accounts then wash it through a fraud filter. If it fails, they will respond accordingly to the merchant site and the sale will not complete.
Did you notice something, though? They made a successful authorization against your card. Here's where things get messy for you. The bank (per their terms and conditions) has now withdrawn that amount from your account. Because there's no capture forthcoming, that money will go back to your account... eventually. How quickly depends on business days and the specific rules of your bank. The company I work for occasionally has people who used debit cards and made several tries with it, not realizing there was a corresponding withdrawal every time. In some cases, they overdrew their accounts with nothing but authorizations. Unfortunately, the bank holds all the cards there with their rules on authorizations. You're at their mercy as to when it expires and goes back into the account. Merchants and their service providers cannot work around that, since they never captured the funds in the first place.
Credit cards with a credit line avoid the problem because the authorization draws against the line of credit, and you're never billed for unsettled authorizations.