While chances are slim, something like this actually happened to a customer a few years ago. They were at a bank that had just installed a new ATM, the ATM vendor left test money in the machine and it went live. I guess our customer was the first to use it and it spit out the test money, labeled with the ATM manufacturer name (I can't remember if it said "Diebold" or whatever on it). I did not believe the customer when they contacted us, but they went right into that bank and the bank acknowledged that it happened. But instead of making things easy on the customer (or us) by just exchanging the test money for real money, they said he had to file a dispute with us.
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"The reason I talk to myself is because I'm the only one whose answers I accept."
- George Carlin