Yes, that concern crossed my mind also...
But, theoretically it is possible to have a multiplayer bank that merges and updates itself - thereby sharing it's information with subsequent players?
In that case I think I will reconfigure the marketplace.
Instead of individual items being sold by individual players. Players sell their items instantly, and amounts sold/bought are tracked in the bank, allowing for fluctuation in market prices. As you play the game more, your character advances and gains access to more valuable items, and as you are playing with more players, the marketplace bank should expand accordingly. Ie, in the early game (with a smaller market bank), most items you find will be cheap but sell to the marketplace for decent amounts. Later on, these same cheap items will be flooded in the market place (as you've played with more players), and lose their market value. I am toying with the idea of there being 3 separate Space Stations with individual markets. So trading can be an effective way to bolster your income - ie. buying low from Market A and selling high to market B.