Most but not all boxcars are always well maintained-
If a door doesn't open or close the customer/shipper can refuse a load or an empty on delivery due to the door not opening, Thus pissing the railroad off cause now they now have to pay for the car to be hauled back to the yard & off to the HOME SHOP FOR REPAIRS.
Most boxcar doors have a latch or lock located on the bottom of the track at the end of the door- look carefully at the mechanics.
I unlatched & unlocked a few boxcar doors to catch flicks of an e2e
Just watch your fingers!