Item Help

[wildfire*]

So, I'm a little confused when it comes to items, their popularity, and how to know if it is a good trade or not. In all honestly, I have a bunch of items I'd be more than willing to trade or donate. But how do I tell what is considered "rare" or in demand? It there a way to tell this? I'm guessing that more of the holiday stuff or C$ is more in demand (correctly me please if I am wrong). But what about other free stuff randomly given out? I'd really like to donate a bunch of stuff to the Lost and Found, but I don't want to miss out on getting some of the things I would like either.
Please let me know! Thanks!

[Puptarts]

you can find rare items on this list,
medieval faire items are being discussed to be put on this list too ^^