Make sure that the instructor knows you are on the first lesson of a full course and not just a one-off trial flight.
Tall guy in a 152,
Well, as far as I'm concerned, you'll get treated just the same, a FULL briefing on the aircraft and Ex 4.1 (effects of controls). You'll be invited to take control and practice after demo of each of the primary effects, then fly the aircraft for the rest of the time, at least to base, maybe final if it goes well. If you politely decline to fly the a/c, well, that's a shame but your business. On the other hand, if you find it getting a bit much and want a break in the middle, that's fine too, I watch out for that; re-assurance and confidence is important.
Obviously for some people it is just cashing in the voucher they were given as a present but I'm sure most instructors are keen to try and convert even these people into students; that's my aim, anyway. We want people to come back.
Fully agree with everything else you said.
Cheers,
TheOddOne