What to do if a spectator wants to use your cards.
I don’t let anyone stop the show AND I don’t make anyone feel bad:
I like performing (sorry I don’t know the name) the trick where it looks like you have an entire deck but you only have about 6 cards, spaced-out, and you tilt them so they look like a deck. Then you hand them the “deck” and remark ‘Wow. You made all the cards disappear. That WAS a good trick” and gesture for the audience to give them some applause.
At that moment you can offer to return when the spectator finds the rest of the cards OR bring-out a coin trick and remark “Since I don’t have any more cards, let’s try this one”. (If the spectator insists that you hand them the cards, you insist-back that they should have them in their pocket… Like we planned.) Now you have the option of continuing with a coin trick or saying that you’ll stop-back in a few minutes when the spectator brings the cards back – and you may leave.
In either case you were not offensive, They didn’t stop the show, and you didn’t make an enemy – if you did it right.
Doing it right means that you gesture for everyone to applaud for the spectator and when you say you’ll be back, you act as if the spectator was “IN” on the trick from the beginning. I conclude by saying to the spectator “I know, that you know, how it was done but if you could do me a favour and not tell anyone else…I’d appreciate it. And again, the spectator appears to have been part of the performance – they got some positive attention and you’re on your way without making anyone look bad.