How do you make credits in ME2?

In Mass Effect, I sold so many guns that I maxed out my credits. ME2 doesn't have that annoying inventory space problem but now it is much harder to get credits. I am constantly broke as I keep spending all available credits on upgrades. It seems the only way to earn is by doing missions and looting and salvage. I have gone through all side and DLC content and there is nothing left but the reaper IFF mission. If I go shopping after the crew is kidnapped, will they get liquified?