There's currently a bug in the game that will make the Melnorme pay YOU 1 credit when you ask him to fill all your tanks up rather than you paying him the appropriate amount of money. Easy way to make money; get him to fill your tanks up, sell all the fuel back off at the Earth Starbase, and run back to Alpha Centauri again; repeat a nauseum. However, this bug will probably be fixed in the next release, so you might wanna get into the habit of saving often to bypass that problem in the first place.
wow, a 14years and (nearly) 2 months necropost....
And by then, Star Control 2 was already 10 years old. I remember playing it around that time, on my 386 16Mhz with 40 megabyte hard drive. Playing it at that time was a really amazing eye-opening mind-expanding experience for a little kid.