"an approach that spares him an embarassing inquisition"
It also clearly indicates that he is guilty, and the price of the fine is cost of doing business to him, so he doesn't care since there are no other repercussions.
On the other hand, this is not organized-crime-level stuff either, so nailing him to the wall would be a bit overkill. The unjust monies have been impounded, that is certainly punishment enough.
So don't do it again, right ?