That line about removing your radiator is priceless!
I haven't had anyone send me back a disassembled item, but I have had people put very delicate and expensive luxury items in a plain letter envelope to return them. It's as though people assume that they are interacting with a machine, so they check their humanity at the door.
Your customer sounds like a reasonable guy who got caught trying to get away with one. I think you're handling it well.