An unGifted Bonisagus

With all the eccentricity tolerated within the Order of Hermes, I'd think it'd be easy to cultivate a fervent reputation for not wanting anyone to cast spells on you. (Sort of like someone who refuses to let themselves be touched. Weird? Sure. Think they're an alien? Probably not.)

I'm not sure it's canon that you can see someone lowering their Parma, though I agree that this bluffing maga would have to at least bluff the timing, if not the Lowering Face. :blush:

The most challenging situation would be for her certamen and wizards war.
Parma magica would be only a threat if a place is protected by a spell with penetration of 0 against mundanes. Magi are expected to have parma and not affected. The LR maker will recognise she has no gift.
The player should present a briliant roleplaying. Will the other players know her disadvantage?

And I'd encourage the player/character to involve other players/characters in the story. The assistance of another magus in the deception is worth its weight in gold... assuming assistance actually weighs anything.

Another magus can extend their Parm Magica around the Giftless magus, giving him the semblance of Parma, weak though it may be. Another could provide enchanted devices, with subtle triggers that mimic the casting of spells, and yet another (I'm aiming to fill a covenant here) could act as champion in any Certamen.

These magi would probably be acting out of friendship and solidarity, though obviously the ear of a rapidly advancing Bonisagus is always useful.

Yes, if I was the player concerned, I'd embrace the other players into the subterfuge rather than trying to pull the wool over their eyes, or the eyes of their characters. The task is difficult enough without making the storytelling even harder.