Ah, retail.

[tanamiya.livejournal.com]

Paraphrased to stick to the point.

Cx: "Hi. I'd like to pick up the computer I just bought that you were setting up for me."
Me: "Certainly. Can I see your receipt?"
Cx: "I don't have it on me."
Me: "I don't have any other way of identifying you to your computer. I'm sure you can understand that I can't just give computers out to anyone who asks for them..."
Cx: "This is ridiculous! I spent $800 here. You can't treat me like this!"
Me: "I'm afraid I can't just give you a computer, sir."
Cx: "Well, then, fine. Here's my credit card. I want you to give me a refund."
Me: "Certainly, sir. I can give you a refund...

...I'll just need your receipt."