The person who packed and declared the goods is the person responsible. However, in most cases, this discovery is only made at the destination port. There's no way to see into a container, other than through scanning.
As I said, if the paperwork has been falsified, as well, you could have a situation. For example, if it says it's a car and the paperwork matches, that's fine. You don't know whether the car was stolen or if the ownership is correct.