Sounds shady. Here's what I think. I think he was planning on "damaging" the grille from the start. He gets the grille, puts a little scratch in it and then makes a claim to you. You make a claim with the shipping and then he was planning on keeping the old grille, getting a new one from you and then selling the damaged one to make up for the cost of the new one. When you made it clear that you are only sending a new one if you get the old one back, you then get the response about how he is trying to assess the value of the damaged grille and suggests half. That's his backup plan.
But, maybe I'm just old and cynical.