Can someone help me out a little here.
So each player has inf of their own currency, so when you get up a shop to "sell things" firstly you have to give everyone some of your currency to spend, (given there is currently no backed currency in my world yet). They can obviously gain your currency by selling stuff to you or through contracts. However you as the player trying get people to use your currency, in your store, you will never gain anything because your personal currency is always inf (up until the point that someone starts minting money).
In short, until someone mints a currency everyone is going to use. You may as well just swap favours? There's no need for a store or tax on your workbenches?