Every time I go to Walmart and get home to check my reciept I find that I've been overcharged. It's usually 10-20 cents over what the item was marked so I never bothered going to customer service to get my money back.
Then I realized, if every customer that checks out at Walmart gets overcharged 10-20cents they are making a HUGE profit on those errors. Now I go (as painful as that is)to customer service and get my money back.
I usually buy a lot at once so I cant stand there and watch each item get scanned. It is frustrating.