I THINK,

Either he's scamming you, or his mail carrier is collecting chips.

You didn't mention if the shipments were insured.
If insured, no problem (except for dealing with USPS, always a problem). If uninsured, you replaced one, this one is on him (equal loss for all).

As far as future dealings, you can refuse to deal with him, or insist on insurance.

From personal experience: I lost at least 17 shipments in a two month period while there was a temporary mail carrier on my route. Some chips got through, but a lot more didn't. As soon as the regular mail carrier returned, I started getting all my shipments again.