Just a couple of questions about seduction.

How likely is it that a significant imperial (say a techpriest or an astropath) is immune to seduction, and how would you tell? Would using Scrutiny after a couple of successful tests allow you to notice that it's not affecting them?

I note that Cold Hearted specifically states that the character is immune to seduction and I understand that other lines have similar talents.

well it really depends the characters social skills and characteristics... Can one hide his cold heart or openly admit it to any one? how good the other to catch signs like emotionless answers social life that equals to zero and such things, also it is a really broken thing to say it is immune to it and nothing to do about it. Like tech-priest and psykers are not common to be obsessed with hunger for more knowledge? Like technological or arcane lores, devices? Using then logic, or deceive maybe charm and say:

Yo techy-priest watch that shiny XY thingy.. Say you do to me X and i give it to you...

(profane yes but if npc, pc also has pride, disgrace or motivation aimed for such thing i think a modified WP test is needed. Of course Cold Hearted can give bonuses). So discovering his/her passion and the lure him such a trap against his drawbacks can break a character willpower to be seduced. Talents and such can give bonuses. Also very unlikely that it's working against powerful Antagonist ,,,,

@Athanatosz

Cold Hearted and its equivalent Chem Geld mostly refer to sexual seduction (and grant some benefits against other uses of Charm). Deceive and its ilk are unaffected anyway.

@Bellevue

I would assume that it's possible to feel out an NPC's reaction to seduction/charm attempts if the character paces himself and doesn't go all-in "Hey, want to join chaos? We've got cookies!" immediately. With a little scrutiny, the character should be able to detect the cold fish before committing himself too openly.

That why i suggested other ways..

Also I'm not a big fun of making pc-npc's untouchable against anything...

I don't see the problem of making it impossible to drown a fish, to poison a stone or to incinerate a Flamer. Some things are just impossible and they shouldn't stop being impossible just because one could use them in a story.

Than good luck that players doesn't fishes, stones and other "creative" beings..

Yup being immune ONE kind of threat is an okay and can give a fascinating edge for a character....