Iiiii personally like the current system? I mean, the problem with adding money to any game is that nobody wants to spend their RP time crunching numbers and even if it's more realistic, it's kind of a pain in the ass. I'd bet people would end up ignoring the currency system the same way some people ignore the credit system.

It would be a lot simpler to just remind people how credits work and let them run businesses how they want? People can just trade items (like the example of someone with 7 credits getting a 6 or less credit person something they can't access) or give whole credits for larger trades. Just remind everyone that credits are worth more since they don't expire or get used up when dealing with the station.