(A customer purchases some items at the checkout. While walking out, he sees a sign that one of his items is on sale.)

Customer: “Excuse me, this sign says this glue is for $4.99, but the shelf says $5.99.”

Me: *looks at receipt* “Well sir, I charged you $4.99.”

Customer: “But the shelf said $5.99.”

Me: “But I charged you $4.99.”

Customer: “But the shelf said $5.99.”

Me: “Okay, give me another dollar.”

(The customer thinks for a second, then walks out of the store without saying another word.)