
My suggestion is about 2 separate features that could also work together nicely and will help keep a server’s economy in check, in my opinion.
1) Server Balance:
A Server Balance (set by the Admin) which will handle the economy behind the shop. The idea is for when players try to buy an item worth $5 for example, they basically pay the Server itself.
So if the Server as another example, has $20 worth of balance and a player sells an item for $5, then the Server itself pays for the item, taking it’s balance down to $15.
This helps a lot to avoid abusive selling, especially in an economy-breaking scenario as it allows to put a stop to it so for the Staff to have enough time to figure out a solution.
2) Taxes
An option in config which will alow to tax each transaction Buy/Sell (together or separetely) via a Tax cut percentage. (e.g. 5% tax based on the price of the item)
This could be connected with the Server Balance idea from above which would give a way for it to generate income from the taxes themselves.