I got a white stripes CD for 10 dollars off because the price on it was wrong. The guy that served me used to have a computer store in town when I was a kid. I remember taking our c64 to him when it had some kind of problem and getting a different one back when he said he couldn't fix it. I don't think he paid enough attention to the things to realise they had different case forms.
We did a lot of complaining and in the confusion somehow ended up with two c64s, both of which worked. I can't remember what we did with the spare, but it was useless because it didn't have a power cord or disk drive. I think we started using it when the first broke down.