Yeah, I had plans to make people buy stuff, but getting certain items was too easy.
Although, I could get around it by offering peanuts for items. So you can sell excess stuff, but you won't get much for it. Mostly cause getting a lot of items like fish, isn't tied to actions. So you could spend 10 minutes clicking, get a bunch, sell them and make a lot of money quickly.
I might add in a Pawn Broker style NPC who will buy certain stuff if you have it (with rotating items). They'll offer decent money, but the items they'll want will vary daily.