charm / dominate question.

[Yqatuba]

If someone makes their save vs the spell can the caster tell it didn't work or no. If no, could the "charmed" person pretend it worked and do whatever the caster says, only to turn on them at an inopportune time?

[Fuzzy-Wuzzy]

Saving Throw wrote:

Succeeding on a Saving Throw: A creature that successfully saves against a spell that has no obvious physical effects feels a hostile force or a tingle, but cannot deduce the exact nature of the attack. Likewise, if a creature's saving throw succeeds against a targeted spell, you sense that the spell has failed. You do not sense when creatures succeed on saves against effect and area spells.

Charm and dominate are both targeted, so the caster can tell.

If there were some area effect version of either, the caster wouldn't know who in the area was affected, so unaffected people could play along if they knew what the caster had been attempting, say from a successful Spellcraft check---as per the above quote, making your save doesn't tell you details of the attack.

[Bob Bob Bob]

The bear (who looks like a tiger?) has the right of it. If this is something you want to have happen though, this magic item exists for exactly that purpose. Specifically, "If the wearer makes a successful Will save against an enchantment, the caster of that spell incorrectly senses the effect has succeeded. Additionally, the bracelet’s wearer knows an enchantment targeted him and the enchantment’s source."