the universal Credit makes things very easy and straightforward, but if it wasn't there, what would fill the gap?
Barter would be possible, and players could haggle - offering to exchange X TCs of Food plus Y TCs of Liquor and Wines for Z TCs of Machinery, and so on. This might make trading a bit more interesting, but in the absence of the Credit it might also be hard to know whether you were getting a good deal or not. And paying for repairs, upgrades, and new ships would be hugely complicated.
Is bartering really more desirable than bargaining? Because if it is the latter that is appealing then it's only set pricing that we need to remove not the currency itself, right?
I think that as soon as you have the concept of currency, be it coins, gold, or a number in a computer, having one currency or many is the same. Because as soon as you have multiple currencies you have exchange rates, either officially or informally.
Agreed. It might be more realistic but it's more complex and in my opinion if it is to be more complex then it needs to be much better.
Having said that, I do like the idea of trading being different between the various inhabitant groups.
A simple way to do that might be to get paid in goods (not necessarily of your choosing). If you're being paid in platinum then that's a lot of food that you need to sell but then not every good needs to be traded at every station.
For a very quick (and not entirely thought through...) example:
Birds - gold/gem stones
Felines - narcotics/platinum
Frogs - gem stones/narcotics
Humanoids - gold/liquor
Insects - luxuries (organic perhaps)/slaves
Lizards - platinum/food (maybe slaves are food
Lobsters - minerals/alloys
Rodents - firearms/food
Food is quite interesting as a currecy: cheap, universally useful and potentially species transferable if it were broken down into it's most base constituents (it needn't be perishable).
Likewise fuel could be quite interesting as a currency (although that could have more serious game ramifications...)