If Charm Person fails...

[taltamir]

I think that if you walk up to a guard and start chanting and waving your hands and he then feels a malevolent force in his mind which he pushes away he should assume you cast a bad spell on him.
Or that you are a witch trying to curse him and that calls for a little lynching.

If you cast a stilled silence spell from across the room while the guard is paying attention to another person and not you, that he might dismiss the malevolent force as paranoia (unless experienced with making saving throws against mind magic) and even if not should not be able to pin point YOU as the source (would be hilarious to do if he is speaking to someone you dislike).

If you use a stilled but not silenced spell on someone he might think it is a spell, or he might think it is foreign language, especially dependent on how you use it (say, turn to your friend and speak the spell) and whether he has spellcraft... whether he ties his "feeling of malevolent force" to being a spell and not just him disliking your "nasty foreign tongue" depends on a variety of factors and can go either way...

As for the whole thing about getting a wizard to buff you and your friends, give you his spellbook, etc... Just because he thinks you are best buddies doesn't mean he is stupid and not paranoid... proper responses should be "friend, I am a bit concerned here, you are scaring me, why do you want to know?" and "I am sorry best friend, but I wouldn't even tell my (non/hypothetical) wife and children where it is hidden, because it can always be an illusion or someone might rip the knowledge from their minds... what if I tell you and then someone casts charm person on you?"

keep in mind that unreasonable demands will be refused, will require persuasion rolls, and might even break the spell if they are too unreasonable.

The spell does not enable you to control the charmed person as if it were an automaton, but it perceives your words and actions in the most favorable way. You can try to give the subject orders, but you must win an opposed Charisma check to convince it to do anything it wouldn’t ordinarily do. (Retries are not allowed.) An affected creature never obeys suicidal or obviously harmful orders, but it might be convinced that something very dangerous is worth doing. Any act by you or your apparent allies that threatens the charmed person breaks the spell. You must speak the person’s language to communicate your commands, or else be good at pantomiming.