Hey Paizo,
I'm pretty bummed out right now because I can't find any way of making my ideas for my character work. I play a Mesmerist who uses a pistol to deliver his Painful Stare (essentially Sneak Attack) in combat, and has very few spells that he uses is combat. In fact, most of his spells focus on manipulating people out of combat.
Here is the thing though: by RAW, using spells without people noticing is INCREDIBLY HARD. It does not matter that I am a psychic caster because magic always has "visible effects identifiable as magic". One way to circumvent this is by using the feat Conceal Spell, but the checks are pretty easy to make, and even then people will know it if you cast spells on them.
Want to cast Charm Person on that boat captain? Think again! Even if he did not realize you cast the spell, he realizes he failed a saving throw and will know he was under the effect of something once the spell wears off, hence becoming potentially hostile towards you. Want to cast Ill Omen on someone before lying to them so they fail their sense motive check? The rules are not clear about whether or not you know if a spell was cast on you when it does not have a saving throw, but you can still make a spellcraft check to realize what spell was cast on you, so it is basically up to DM discretion!
My point is: I wanted to use spells that influenced NPCs around me without them ever knowing (fitting for a MESMERIST, right?), but there are so many rules stacked against me that I feel like I should just give up and take utility spells instead. My DM is not open to suggestions about letting me cast spells incognito unless it specifically says in the rules that I can.
People of Paizo, can you help me?
If you'd rather oppose their perception checks with bluff than sleight of hand, cunning caster is an option. That also gets to add bonuses other than ranks + ability mod. People don't actually know that you've cast spells on them if they fail their save, and even if they make them you might get the subtle enchantments feat to have a 50% chance of them missing it.
Using Charm Person etc. can have consequences; I recommend a disguise. If you want to be Mr Nice Guy who never has things like that happen to him try buffs instead, spells like Glibness.
Cunning Caster is a much better feat for psychic spellcasters to hide their spellcasting. Significantly better than Conceal Spell. If nobody knows you cast a spell at all, they have no reason to roll a spellcraft check.