let's say i do shapeshifter, after i'm done they go "no way" and then grab at the cards to see if they can guess how it was done.
I rekcon you should have a couple outs on hand, based on where you're at in your routine. Ask yourself what you are left with after a trick or a mover and what you need to keep going (if you're in the middle of your routine).
In your Shapeshifter example, I see two options. Assuming you have your deck in hand and have just made the move.... return the
you know what to the top of the deck and then hand the face up card out to the spectator and then quickly, but casually, perform a swing cut. If they want the deck you can hand it to them or you can say whatever you want get say no. If they are close to you and are seem grabby, do this: when you are ready to hand the face up card out for examination, angle your body so that you have to reach over your deck holding hand, thus covering the deck. While protected, do a charlier cut (SP?). Again, you're now clean and ready to deal with the spectator.
Like I said, what do you want to do. Be able to hand them the deck? Do you need to retain a packet or a stack or something? Do you want to stop the routine altogether? Do you want to be able to say no and continue? Come up with a couple outs based on your routine and what
your desired outcome is.