First of all, don't go to India you'll have 4 people telling you your doing it wrong before you can get the clutch out in reverse and that was just with a delivery truck.
Second, I use my son or no one its just easier that way.
I have never offered help anyone back up their own trailer. I have yelled to stop them from hitting something but that's as far as I go, without being asked. I figure they wont learn unless they do it themselves.
The exception to that rule was last month the building next door to mine is a racing go cart shop. And they borrowed a 30' goose neck 5er race trailer and truck to take all theirs and another guys stuff to Vegas for a race. When they brought it back the father and son were trying to back it in, Very long driveway with a 90 degree at the end and VERY tight to park even when the lot is empty. So after about 15 min I came out offer to move our cars to make it easier, he promptly got out and said "you have a trailer I've seen you put it in hear before here's the keys." I took the keys, nervously, and backed it in (it looked pretty good), and I never told him I've never backed up a 5er before.