If there was no damage to the shipping box and it was packed properly, he broke it.
If it was damaged in shipping, as in the shipper played kickball with the box it was shipped in it is their fault and shipping insurance would pay him up to $100 or something like that.
You should have told him to take up the issue with the shipper because it is not your problem, you shipped him a perfectly intact part.
By accepting the part back you accepted the liability of making it right- it was your fault so you get to eat the costs.