A while back, I discovered you could raise an item's quality from Common up to Uncommon by selling it, reloading, and then buying back that item. At Level 50, I've since discovered that same trick can even add new mod slots to an item that had none at all to start with. The problem is that this is somewhat random. Sometimes you get one. Sometimes you get two. Sometimes you get Epic. Sometimes you get Rare. Still, if you're willing to spare the Eddies, this can save you from having to farm an area dry a hundred times over.