I would lend out my Singer 237s - they are very basic - the down side to them is that they are heavy. The sewer would have to sit still for a "how-to" on how to thread the machine, winding the bobbin, how to insert the bobbin, and how to change the needle.
If the person is not willing to go through that part of using my machines, no deal.
I won't even touch some of the newer, fancier machines for fear of messing them up.