There are times when wise spectators either lie or refuse to say.
Magi: "...and what was your card?"
Spec: "Er, I forgot.
You tell me, your the magician!"
To rule this out common with mind effects I usually have a card sighted, noted on an blank index card and verified with another stranger spectator. Then I can have a third spectator read the first specatators card value.
When I am a specator in a large audience of another magician's show, I tend to make sure I remember the card and say the correct response as I feel it is the right thing to do otherwise I'd be upsetting the show. I can understand it could not be an easy task for a nervous spectator.
I wonder if anyone on this board has forgotten, lied or refused to another magician about their sighted card.