The Tale of the Non-Believer

A normal Sunday at the laundromat. A lady comes in to pick up her dry cleaning. I notice that it is a hefty bill of around $60, which is a fair amount for dry cleaning. I ring it up. She hands me a credit card. I swipe it, type in the amount being charged, then hit Enter. At this point, the telephone begins to ring. Since the phone and the debit machine are on the same line only one can work at a time. So I decide not to answer it. The phone eventually stops ringing, but the charge hasn't gone through yet. It's obvious that this lady is either in a hurry or is PMS-ing. Finally the machine says "Line Busy - Request Cancelled". I give her back the receipt, saying, "It didn't go through because the phone was ringing. I'll need to do it again."
"No!" She is completely appalled.
"No?"
"I don't want the charges to appear twice on my account!"
"It won't. It didn't go through the first time. See right here? It says CANCELLED. Besides, if for some reason you do get charged twice, you can take this receipt down to the bank and they'll fix it right up."
"I'm not letting you swipe my card again. The TV said you shouldn't ever let them swipe your card twice."
"Look, I promise you that the first one didn't go through. See, the phone runs on the same line so it interrupted the signal and it couldn't send the charge. If I swipe it again I promise it won't appear twice."
"I'm not letting you swipe it twice." I make a few more attempts at convincing her. She is angered. "This is just wonderful!" she snaps. "How am I supposed to get my fucking dry cleaning?"
Eventually I convince her. I guess she was desperate.
"Okay do it, but I want you to sign this receipt!"
"Fine." I sign the receipt and swipe her card again. This time, before I pressed Enter, the phone rang. Crap, I thought. Since last time I had pressed Enter before the phone rang, I knew that if I hadn't pressed Enter yet then answering the phone would be all right. So I answered the phone. It was my boyfriend, so I told him to call back.
"I suppose that one won't go through now!" she snapped.
"No, I haven't entered it yet, see?" I press Enter. Charge goes through perfectly.
"Make sure I get a receipt!"
I give her the receipt.
"I want the one from the till!"
At this point I would have given her money to get out of the store so I didn't ask why she wanted the useless till receipt. I printed it off, stamped the back with our stamp and gave it to her.
"What kind of piece of crap receipt is this? It doesn't even have your name or phone number on it!"
"I know, Ma'am, that's why I stamped it on the back."
She turns it over.
"Oh."
And she is gone.