I noticed (and think its very cool) that NPC Merchants have an Inventory with a max number od X product they will buy.  Taking that a step further it might be cool if the price they pay for X item chnges slightly based on the NPC's inventory. For example, a "Cure" scroll nets me 25 Gold across the board. Would be interesting to maybe only recieve 10 Gold when the NPC is at the top 10% of inventory max or 35 Gold at the bottom 10%- If that makes sense.