She should never have put the store on blast, but the store owner shouldn't have responded publicly with a snarky, one-upmanship-filled message that escalated the situation.
"Nothing happened to justify her scolding our employees like that on her way out, but I could let that go..."
He didn't let it go, though. He doubled, tripled, and quadrupled down. Now he's playing the victim.
All he had to do when she first posted about it was publicly say, "I'm sorry you left our shop feeling disrespected. It was a gross misunderstanding, and we humbly apologize. We would love to connect you with the artist so you can purchase one, or, if you prefer, we would be happy to sell you one of the German versions for about $ 2,000.00. Again, we apologize for the misunderstanding and appreciate your business."
Not too difficult. Business 101 stuff.
It saddens me that no one who cares about him or his store has told him this at any point.