Because it's assumed that if someone trusts you enough to post their quiz log in, you won't change anything of it and will just use it to boost your account. But there's no way for anyone to keep you from, say, changing the quiz's contents or the password.. It's just assumed you won't out of respect and courtesy for others.
That's what an honor system is; it relies on the honesty of others.
Question: How the heck are Newbies starting at Novice with pictures? I'm not talking about the Newbies having pictures you gave them. I've seen accounts just pop up at Novice with no record of anything and they have pictures. They're mainly the faker accounts, but still? The what heck?
Spice made a second account, and she leveled up to novice by linking one of her quizzes on her Spice account. After a few minutes she somehow got down to newbie, and she said that she guessed she had to keep linking the quiz to stay at novice. She still had her picture, though, at newbie.