The reason could be just to take a picture of the VIN to attach to their paperwork and cover their tracks. Hopefully, the tractors also pass through radiation detector testing.
It serves as an unofficial fine for NH - requiring transporting the tractors again. The official fine would be 5-10 times as much.
My guess is anything official would ultimately require someone in Customs to explain why 53 loaded trucks left the Port of Entry without their knowledge or prevention. /forums/images/graemlins/blush.gif