Barbs aside, lets put this situation on a more personal nature.
How would YOU feel if you went to WM, bought oil, and as you were pouring it into your engine, realized it was used oil?
You'd be furious about having to drain your engine, get to WM, and convince them they sold you a bottle of used oil.
You'd be cursing the guy that did this to you every name in the book. You'd swear you'd NEVER do that to someone. You wouldn't laugh it off or dismiss it......