Ditto to both posts.
One other thing...my experience working at a Veterinary office showed me that people respond very quickly to SALMONELLA. Even though the risk is exaggerated, just the mention of turtles carrying salmonella will often discourage people from keeping them. There's plenty of "scary" turtle/salmonella information on the internet for you to print out.
I've been prone to exaggerating the risks of salmonella when the future keeper is blatantly disregarding basic care requirements..."Can I keep a Painted turtle in a dry box and just let it swim for a few hours a day??"