Requirements to buy a wheelchair?

I was just wondering, if you go to a store like Rite Aid, you know how they have those wheelchairs there sometimes? Can anyone just go in and buy one? Or do you need some sort of medical disability to buy one, like a wheelchair license or something? same with the canes they have there; do u need a medical disability to buy one? I was just curious, because maybe a person is clumsy and just wants one to have around just in case you know?