About all a shipper does is provide the item/s to be shipped and pay money the agent sometimes called a dispatcher does indeed arrange for most permits but not always, many haulers operate as independent contractors running under the flags of which ever trucking company they are leased to. In these cases a hauler may use the resources of the company's assets through their dispatchers and agents to arrange for their over dimensional, and special use permits or they might contact permitting agencies direct. Then again not all permits can be pre arranged in all states by a single or even multiple permit issuing facilities. there are still some states where the permits may be applied for in advance but must be picked up at the ports of entry. Ultimately whether a driver is hauling a load of dispatcher brains IE and empty trailer, hauling a single gram of something that will destroy all life on earth or trying to haul something the size of the State of Texas the final responsibility to make sure everything is all legal with the "T"s dotted and the "I"s crossed belongs to the guy with the steering wheel in his hands.