Have to say that I'm now with Whirly (and many others on this thread).
The trial lesson was always done as a "taster" - 99.9% of which was a thirty minute "jolly" during which it was my aim to make the flight so much fun for both the "student" and (mainly) his partner in the back.
I used to go to great lengths to involve wife/girlfriend/partner (whoever) and get them to come along and enjoy the ride. If the student did pick it up and continue with a course then they, as a couple, had to justify spending £4,000 on aeroplanes rather than on a new kitchen or a holiday with Mickey Mouse.
I, myself, was one who went for a "pleasure flight" - which was sold as a pleasure flight, not a trial lesson at Leeds/Bradford back in 1977. I turned up at the school and asked for the advertised price. They explained that they needed three people (at the advertised price per seat) to make it worthwhile flying the aicraft. I asked "Can I pay for all three seats, then?" at which point they said, "Well if you want to pay for the full aircraft then you should do a trial lesson and then you can have a go at flying it yourself".
I enjoyed it so much that as soon as we landed I signed up for a 40 hour PPL course.
I always flew my trial lessons in exactly the same way - give them so much fun that they signed up for the course - and that's why I gave no deep rooted briefings on EoC, Theory of Flight, Exercise 1 and 2 (as this first one was 3 - go figure) etc. Most certainly NOT aerobatics - though I could see why somebody would be interested AFTER the flight. I taught them NOTHING - just let them play and pointed out a thing or two.
The majority of people did sign up for further lessons - many completed and gained their wings, some dropped out before the end. Well, at £40 an hour it's to be expected, don't you think.