Flying for fun. Sorry about the spray old chap - I was quite wrong and should not have replied in such a boorish manner. Having said that the problem is that a brand new potential student eager for a trial flight, lacks the experience to know if his flight will be a bumpy windy one or just a nice pleasant day with a lovely view. He may say he still wants to fly but is this just bravado or simply loss of face to pull out? It is entirely the instructors responsibility to take care of his well being. Once airborne your student is captive audience to whatever the weather dishes up and in the worse case he may heave his guts out and never want to fly a light plane again.
Many years ago I was offered a ride in a yacht. The yachtsman (a qualified airline captain, no less) assured me that 30 knots surface wind on the bay was absolutely no sweat. Despite misgivings I was too embarrassed to say no thanks as I was the one who had asked him for the ride. Foolishly I went along with his undoubted enthusiasm. Of the 23 yachts that entered the race, 20 withdrew after an hour due to appalling seas. My captain was a yachtsman of some international fame and he stuck it out and won the four hour race.
I just about died of sea-sickness and nothing will ever entice me into a bloody yacht again - ever! Don't put an inexperienced but enthusiastic student pilot in the same boat - geddit!