It's an easy mistake to make, please let it go. If you can get a break out of them, that's fair, but it wasn't an intentional thing. Some kid screwed up and sold what he saw as simply inventory on the sales floor. If the builder/mechanic didn't clearly mark it with a "SOLD" sign, it's not the sales guy's fault. Where I worked it sometimes got so busy that things like this could easily happen just because everyone was trying to do their job right and make customers happy.
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Tom
"It hurts so good..."