Well, i wouldnt ignore them, but i wouldnt say no eather. If you do one of those, they are bound to know it is gimmicked. That is why i dont work with gimmicked decks. If you can get around them at all, then do, that spares your time and your name.

I usually extend the deck to them. Just before they can take it I pull it back, smile and then say, "That's enough". This gets a laugh and usually diffuses the situation. LOL

Ok, you wanna hold it? Here you go.

Now show them a contract saying that you are not responsible for any harm or injury you get while you are examining the parts of the magic trick. And if you damage the item in any way, they will have to replace the item.

Make it unusually long and boring, and while they're reading it, you can do a switch or something...

It doesnt have to be a gimmicked deck for u not to want them to shuffle. it could be with a regular deck of cards and have a setup

Do this.

Say that you can shuffle it in a moment.
Palm off the card and do a one handed shuffle to draw attention away from your hand and place the card in your pocket. then, hand him the deck and "say now you try". place the deck on the table and show your hands empty. then say, "or shuffle it how you want." when they are finished, say "and little do you know, that the card is on top." when you see that it is not their card say "well look what you did, you messed up the trick, the card is no longer in the deck at all" and spred through the cards to show them. place the cards in the same pocket as the other card and walk away.

This is one reason, as a card magician, to master at least one false shuffle and one false cut even if the effect doesnt requires one. In other words, some sort of a convincer.

----

I usually try to make a humorous comment and move on with the trick(or on to another trick if I had just finished one). Of course, this is hard to do when a girl reaches out and grabs my cards after 8 Card Brainwave. Shame, no one wants their minds read these days.

i say
it's magic, only i can contain it. if i give it to you it'll dissapear

What I do is glimpse the card on every trick where they have a free selection, that way if they decide they want to shuffle the deck you just do a different effect. It may not be what you've planned but you still come out on top and don't look like a bumbling idiot.

i just palm it off let them shuffle it, then put it back very simple.
Usually though its not neccessary,spectator=let me shuffle the deck
you=ok
spectator=im just playing
that usually happens if not use the first method.

If you have a good levitation effect, when they say "can i see____" say what? i didnt hear you and when they start to repeat it... start to levitate. That should keep their mind off of the gimmicked _____. you can also say "sorry, first ill need a search warrant"