Still don't know where you're getting that. There seems to be some fundamental disconnect somewhere. If you're not literally telling them "NPC is trustworthy" or "You believe the NPC" then you're probably okay. If you're honoring their action declaration as I laid out, then it's all good. If you're rolling Charisma (Deception) for the NPC because they lied, establishing uncertainty as to whether the PC is influenced, and expect the player to play as if they are deceived or telling the player they must do so, then that goes against the player determining what their character thinks, does, and says.
See, I disagree that this is telling the player what their character thinks. Instead, when I roll for Deception, I am rolling for what the PC
experiences. "He seems honest."
I think what you're put off by is that people tend to use sentences like "you think he's lying" in a way that (edit: you think) means the player
can't choose otherwise. But that sort of phrasing isn't mind-control. It's just a shortcut, like saying "you don't find any traps on the chest." That doesn't mean there aren't any traps, and it doesn't mean the PC
has to open the chest. And you don't
have to trust an NPC just because the DM says "she seems honest." People use that "you think he's lying" or "she seems honest" because--as I pointed out--
only giving the physical descriptions of the NPC like "he's fidgety and contradictory" doesn't always say what you intend it to say. Is a person's fidgetiness due to lying, nervousness for other reasons, a personality trait, or hemorrhoids? Are they contradicting themselves because they're lying, because they're a crappy storyteller, because the events were convoluted and possibly magical in nature, or because the DM made a mistake? Use a description
with the phrase "you think he's lying" if you actually want to get across a message
clearly.
(This is also why I don't like the advice "always trust the DM." No, the DM should be honest in what you experience, not in what things actually are like. Your PC's senses
can fool them.)