I'm not an author, but I'm pretty sure that if you give something out as fan fiction you won't be able to get it officially published later.
I'm aware of that. I'm just writing them now, sending them later. I let others read and critique them, but that's usually it.
There was this one guy who wanted to keep a copy of a short story of mine (and there was also my uncle), but that's it. And I trust them. They won't try to sell'em.