I have a lovely neighbour, careful and considerate. He apparently had a Broads hire a while back, he will not repeat the experience because he couldn't moor it. Now he is a practical and intelligent guy, did he get a good briefing? I bet he didn't, and he won't be back; which is a pity because skippers like he could have been are surely more desirable than more casual ones.
Vaughan, you have experience in spades, and clearly did the job properly; my suggestion was that theory of mooring and a safety briefing should/could take place separately, the trial run can then build on this.
Some won't and some can't pay attention, fair dos but stress blocks learning big time, so some off-boat makes sense to me.
We hired lots, and were always aware that the boat was a pricey bit of kit, I think boatyards could save money by better tailoring their briefings, fewer interesting happenings...more respect for a boat with a message going out that the yard has invested time to underline how to approach the experience.