Jacjet,
I don't think there is anything wrong with that. However, at my field you may have some stiff competition. Since I have my own trainer, radio etc.. for people to use, and will provide the fuel (most will offer to pay the fuel, if they can't afford it they shouldn't be flying), and I won't charge anything.
However, since they have to join the club, I guess that means they are paying for someone to teach them after all..
In fact, no one is going to make a living at that, most will have a full time job. And I agree with RCCC. It is hard to get someone at the field on short notice, when you suddenly have some free time. But that can even happen with a paid instructor, they are usuall not available 24 hours a day. But, I have already setup a time for tomorrow with someone to help them out. He has no plane, and I will teach him on my plane until he gets confident, then he can buy his own plane.
But can you really teach someone to fly in just one hour?