I am fairly new to D&D; however, I have years of roleplay experience. Last night I attempted to charm a shopkeeper, and the DM didn't tell me if I succeeded or failed — he seems to do this with everything. Anyway, having read the description of charm person and then reading several views on it by others, it seems the common consensus, if the NPC passes the save and is not charmed, is that nothing should happen. However, what happened is this:
The DM told me the shopkeeper's eyes started to glow slightly and to tell her what to do and so I asked her to give me some potions. I understood it as though if her eyes changed then yes, she was charmed. Apparently this was not the case and she pulled a crossbow out on me instead, so I left the shop. I really think I've been cheated here, but I want your opinions as I'm unsure whether I need to talk to the DM or not.
Like I said, the common consensus I found is that if an NPC is not charmed then nothing at all should happen until the spell ends, when it says they know they are charmed, but they have to have been charmed in the first place to know this.