I overheard this conversation yesterday.
Potential Customer: Do you have Product X, and how much is it?
Shop Keeper: Yes, it's £99.
PC: Your competitor, on the next street, is selling it for £80!
SK: Why don't you go and buy it from him then?
PC: He doesn't have any in stock.
SK(sarcastically): If I didn't have any - I'd sell it for £70...