I don't get it. If he knew his gun took 4.5mm, why would he order 6mm ones that is clearly labeled on the package in the picture?
He wasn't a dick about it, so that's a plus. Id say refund him his money and tell him to be more aware of what he is purchasing next time. I'd ask him to count the BB's just to make sure they are all there as well :P
Sadly stupidity is not a crime, but it damn well should be. If it weren't for these people I'd be out of a job.
I personally never buy anything without a picture attatched to it that is decent quality so i can inspect it throughly.