I have the fine folks at Safeway to thank for supplying the official caffeinated beverage of the Punny Money 24-Hour Blog Marathon. That’s because an error appeared on my receipt when I stopped by today; instead of charging the sale price of $1 for a 2-liter bottle of Vault, their computers assessed me the full price of $1.69.

I noticed the discrepancy right after swiping my credit card, but I completed the transaction and moved to the customer service desk so I didn’t hold up everyone else in the express line. Like many grocery stores, my Safeway has a policy of refunding the full purchase price in the event of a pricing error against you.

If your store has a similar policy, it can really pay off to keep an eye on the prices for which your items scan. Don’t hesitate to question any transactions where you’re not sure if you received the correct price. And before you walk out of the store, take a quick look over your receipt to see if you spot any obvious errors. You might question whether a 30-cent error is worth the effort of getting back in line to get a refund, but imagine how much money you could lose over the course of a lifetime to such mistakes.