actually I dont think very many merchants use any scripts for transfering morphs, the transfer programs such as Morphing Clothes do a very nice job but in general its not clean enough for commercial work. most that I know of do it the old fashioned way, either hand sculpting the morph in their modeler, or using magnets in poser (I prefer the hand sculpting route in C4D which has a very nice magnet tool).

As far as making clothes loose, some do I guess, but that can run into its own problems, because tighter clothes tend to more precisely duplicate the figure's joint bends, and it doesn't look realistic for a lot of clothes to be too loose.