If you don’t do this, I can guarantee you’re paying more for items. I notice a mistake at least a couple times a month on my groceries. Most often, the price is incorrect in the computer. And, yes, I’m one of those annoying shoppers that will make the cashier send the bagger to go and check the price on the tag. and I would suggest you do the same! You can also grab the sales ad and keep it with you and show the checker if it is in the ad. But, PLEASE, don’t spend more for an item that the STORE is advertising is on sale.