Knowledge and Imagination

When it comes to materialistic things, Plato states that users are the only ones who can tell the makers whether what they make is 'good' or 'bad'; the makers simply follow the users’ instructions to make a 'good' thing. When it comes to this, though, what if maker and user are one in the same? Can it not hold that (to use the example from The Republic) many flute makers are also the users of these flutes?  How would Plato explain an instance such as this? Following this belief of Plato, craftsmen and artists (as makers) can never know if what they imitate is good or bad as they have no real knowledge or proper opinion about what they are making.  
To go along with this and to address a topic we temporarily discussed in class, what does it mean to have a real 'knowledge' of something? Socrates states that “some people...say that if a good poet produces fine poetry, he must have knowledge of the things he writes about, or else he wouldn’t be able to produce it at all.” I find a huge flaw with this point; even if all things are simply imitations of the real Forms, one doesn't have to know about it in order to create it. How would someone draw a tree if they'd never seen a tree or been told what a tree is supposed to look like according to the predetermined characteristics of what makes a 'tree' in our realm of existence what it is? A tree in my mind may look different than a tree in another person's mind. On that same note, how would someone create something that is based off of something in their imagination but that has never been materialized in our realm? To use the example I raised in class, where did the idea of fairies come from? I'm sure creators of legend and folklore never actually had any direct knowledge or experience with fairies. I actually liked the way Alex put it in class--that what we create in our imagination is actually a misunderstanding of the Forms. Is it true that our imagination just tricking us?
In The Republic, Plato somewhat contradicts himself with these ideas. With one point he says that users of things are the only ones who can ever know them; on the other end, though, he states that makers (artists) must know the thing they are creating in order to produce it.
I don't know, Plato, but it seems to me that you didn't fully think this one through...