Roger made a comment in the thread of a member having a problem getting the coupler locked on a new trailer that jogged my mind. He said if someone else touched it....check it yourself.
I retired from a large utility company and we had 100's of trailers. I had a rule that I passed on to many new employees about towing. If someone else guides you back to hitch up even if they do all the connections, always recheck them yourself. If I backed someone up the only thing I did was to drop the trailer on the ball or pintel, no chains, air brakes
or electric and always told the driver to finish it up and check everything including the load. The driver was responcible and the company surely didn't need a deep pocket lawsuit because they thought the other person hooked everything up correctly. Must have worked as I never heard of a problem.
I do have another kind of funny story from work way back that has transfered over to the way I tow/check now. The trailers I used during work were almost never disconnected from the trucks my unit used. One day on a job one of the guys disconnected my trailer. We finished the job and went to move on to the next one. Of course when I looked back after 100' my trailer was still sitting there. It was funny and only took a few minutes to hook up again but it did make an impression on me. Always did a walk around after that. Any time I stop now, fuel, rest or whatever I always check the hookup and feel the axles for temp as most of us here do. I also tow a Manx dune buggy with a towbar. Anytime I stop and am away from it, I alway check to make sure some yahoo hasn't thought it would be funny to put the car in gear before I move. That happened to a friend of mine, big bucks to fix it. Anyway, that's my story and I'm sticking to it