Sometimes they even admit it:
Definition of “a little”:
There were some really nice Braeburn apples but they were $3.99/lb, I refuse to pay more than $1.99/lb for any fruit except berries. So at the self-checkout I punched the button for Red Delicious apples which are $1.69. Am I a horrible person or does pretty much everyone cheat once in a while?
No, you’re a horrible person. And a couple of years from now, when you’re whining about waiting tables and being stiffed on a tip, you might want to remember this little incident.
(Title via She & Him.)