From a slightly different perspective, you need to convert the credits into an easier to use currency, as an example, converting hundred dollar bills into ones, fives, tens, twenties, whatever. Assuming your gals are smart enough, it shouldn't be hard to get full price for the credits, it's just a matter of going to a bank or the equivalent and converting them into more useful types of money, choose well and there shouldn't even be a service fee.
What could be fun is looting different currencies, used by some of the smaller factions or magacorps of the setting, that converting into useful cash does require dealing with conversion costs. Like the NCR dollar to bottlecap, from Fallout. It might even be possible to make the exchange rates fluctuate, allowing you to try to wait for a profit, though probably that's far more work than anyone really wants to do.
