I think you have it. In my games the telegraphing of NPCs that are only interested in money comes primarily from the conversation with the PCs. I also provide bits of information on NPC body language based on some passive insight scores. Often times, the NPCs will try to escape, and say something about not getting paid enough for this job. In the case of cult members, they stick around an say something about the PCs being crushed by their favorite god.
I also use passive perception, character race, character background, etc. to give tidbits of info regarding the environment. For instance, in the case of the dwarven made magic items, I would let the dwarf player know that these are clearly finely made dwarven items. No check is necessary.
