I know this may seem a little vague, but I recently came up with an idea in which a player can buy shares, or sell shares of a company (NPC Shop). The price of the share will vary depending upon how many people purchase an item(s) from that NPC.
I don't believe the increments should be random, but around a certain increment whenever it decreases or increases. I was thinking the rate for the increase in the share price should be, after every 10 people purchase an item or 10 items are purchased from this shop, the share price increases by 5k. If within 1 hour, no one purchases an item or not as many, the price would decrease by 5k.
Now, what would you do with these shares? As the price increases/decreases, thats the amount you are able to sell it for, to other players. I guess you can call it like idle money, but also as a gamble, because your shares can either increase or decrease depending on what the HH population does with these NPC shops.
Although the Book Store/Library seems almost like the most visited NPC for purchases, it would be exlcuded. The Pet Shop, Bartholomew's, Viper's, Carter's Coconuts, The Fairyville Shop(forgot the name), the one in Heaths Training Grounds, PvP Arena's shop, Geraldo's Foods, The NPC Shop in petropolis and finally Fishing Fort, would all be included on the list of NPC's that you can buy shares from (for their company/store). Is there a shop I am missing?
(Edit) Shares should/would not take up inventory space, but instead would have its own tab in which you can own up to 20 shares.