I believe this has been suggested before (Maybe by Gyururu?) but, I thought i'd bring it up anyways.
Some people buy things that they just don't want. Plain and simple, I have and so has everyone else in this game. Well, what if there was a shop that would buy anything from you at a reduced rate? They could sell anything from collectibles to poisoned kunai. Of course you wouldn't get near what you originally paid for them. I myself am not very fond of this idea which is why im not going into detail about it. Although if I get some positive feedback i'll write something up.
Leave some feedback!