I would just add something like a compound daily tax on trades.
If the trades are small enough and not that frequent, which is how I'm guessing real trade will be handled, it should just seem like another level to the complexity of your game; like its more realistic.
For larger and more frequent trades, those taxes will add up, forcing the multi-account holders to have less revenue than they could and in turn holding them back from steam-rolling the games legit players.
Boom.
Okay, but, why do the players even want money then? Why would I accept it as currency from another player (instead of demanding some kind of goods as a barter) if I can't turn around and spend it somewhere?
?? You can spend it anywhere you like, as long as you aren't clearly pooling it with other characters. That and you don't have any other choice. Goods can only be bought/sold with money. There is no trading of goods, only goods for money. Players can't give goods to each other in any way but a "contract" that says these goods for this amount of money, OR via a marketplace which is the same thing but an automatic "contract" that doesn't require players making manually. The player contract way is sort of a pain so it'll speed up the development of people making marketplaces to make buying/selling easier.
Making a "contract" manually isn't hard, but you have to seek people out that have what you want and then negotiate a price. That's a pain, and it's just easier for sellers to put up goods on a marketplace and buyers to search and buy there. The manual way would be to get near another player, and right click them and select Buy Goods or Sell Goods, which opens up the dialog where you or them can put money and the other puts the goods. There is no way to trade goods directly. The game doesn't allow it. That's why money is important.
Ahh, no 2-sided trading, gotcha. It's been a long time since I played a game that didn't have a trading interface where both players could add both items and money (or no player-to-player trading at all) so I forgot about that possibility. It will be interesting to see how that works - whether people who have been playing longer tend to hoard currency to force the value up, or whether new players tend to spend their currency then have great difficulty getting it back, or whether new players tend to end up working for a wage for older players, or what.
It will be interesting to see how that works - whether people who have been playing longer tend to hoard currency to force the value up, or whether new players tend to spend their currency then have great difficulty getting it back, or whether new players tend to end up working for a wage for older players, or what.
This is why I'm making this game. I feel it'll be a fun game to be a business owner and build a virtual world with other players given these "laws" and see how it turns out. It could go horribly wrong lol, but that's 1/2 the fun I think. People could be talking about living through the great depression of 2016 in this game 
I would allow players to write stories/books for others to read so history of the game can be recorded. I can even make major events holidays. I want lots of fan interactivity in the progress of the game. New patches will provide new inventions that make lives easier and even possible change the market around for resources that were once not as important! I want players to vote on what new craftable things they would like.
@Dave, that tax idea is interesting. I could tax both large and many transactions in a short time span with the same players to a point where it doesn't become worth it. This would promote diversity and smaller transactions. I would have to just balance it to make sure it doesn't become a problem. The buyer would pay the tax. I think this combined with watching for cheaters would help minimize a player from steamrolling like you say.
