A young man goes into a liquor store and approaches the shop owner.
Customer: "Excuse me, can I ask you a question?"
Shop owner: "Sure, son, go ahead."
Customer: "Why are you selling the Jack Daniels at thirty dollars per bottle?"
Shop owner: "And why shouldn't I, exactly?"
Customer: "But the owner of the shop across the street sells it at twenty dollars per bottle."
Shop owner: "Well, if you don't like it, why don't you go and buy there?"
Customer: "Well, because right now, they don't have any Jack Daniels."
"I assure you young man," said the shop owner, "once I run out of Jack Daniels, I'll be selling it at fifteen dollars per bottle!"