Don't worry, it's something that has concerned many of us. Over time, with experience, and by watching other magicians, I've realized that no one is immune to it, and there are several ways to tackle the issue.

First off, let's talk about preventing it from happening. There are several ways to do this. As others have mentioned, starting with a self-working trick that builds trust or deters overly curious spectators is one approach. Other great options include starting with an impromptu effect that allows you to have the deck thoroughly shuffled. Even emphasizing before and during the trick that they should keep shuffling (even if partially), and constantly reminding them. A good gag can work wonders, something like: "Alright, let's form a new society of card shufflers!" or similar. Later, when it suits your purpose, you can mention it, and people will feel like they've shuffled till they're blue in the face. Once they've tired of shuffling, the chances of them asking you to shuffle again are minimal. You might even offer to have the deck shuffled, and they'll tell you it's not necessary, that it's fine. Another option is to start with a trick where you have them shuffle while maintaining a small stack on top. There are very subtle techniques for this, and if the spectators keep shuffling, you'll still achieve the same result. By the time you get to a trick where you need a control, no one will ask to shuffle out of fear of being bothersome. Other "pre-game" options include having them shuffle and then doing a deck switch. Or you could introduce a second deck in a two-deck routine where it's not shuffled, but the feeling is similar. People get tired of shuffling and won't ask again, perhaps out of politeness or just being "shuffled out."

Another good approach is to prevent it from even coming up. If you perform a trick where the patter isn't interrupted to have a card selected and returned, but rather that action is integrated into your patter, people will naturally accept it to avoid interrupting you, and no one will stop you to ask for a shuffle. In case it does happen, there are two excellent options. I've even seen magicians like Tamariz or Matas do this. Simply hand the deck out to be shuffled naturally, with a "Sure, go ahead!" or a gag like, "Oh, that's what was next! How did you know? Are you a magician too?" You hand them the deck to shuffle, and confidently ask them not to forget their card, as it will be crucial later. Then you just move on to another trick; problem solved. Later, you ask them to name the card, saying the moment has come, and perform a trick with that card. Something like, "Now's the big moment, the moment for your card! Which one was it?" You openly produce it and perform a sandwich effect or a 'Hunters' trick, and everything's resolved. No one knows what you were going to do with that card, and they won't even consider that you might not have been able to control it. You can also switch to this option directly instead of saving it for later. If you say something like, "The important thing isn't your specific card; its identity could be anything. Just tell me, don't worry, I can know it too. What's important is what the Kings are capable of doing" (and then you go into a 'Hunters' effect, for instance). These kinds of quick pivots are something many magicians keep in their repertoire, and they work best for these types of situations. Better than a Palm or anything else. A Palm, when not properly covered within the routine, is like walking a tightrope without a net. If it's spotted – and the chances are high with an isolated move – the session is over. The audience will switch into "suspicion mode." But no one knows what you were going to do with the selected and returned card except you. You can change direction, play it down, and continue with a session full of magic.

Sounds like you might be a bit of a beginner. I only say that because it's a question I used to ask myself when I was starting out. You see, the Palm isn't an easy sleight, and you can really blow it if you get caught.

If you suspect you've got some challenging spectators in the audience, you can start your set with a couple of self-working tricks or a gaffed deck to help them relax and for you to build confidence.

Hey @Anonimous_zombie

If you're already "controlling the spectator's card," then the hard part is over. 😊

For example (the simplest one):

Control it to the top or bottom, palm it (take the card wherever you want), hand over the deck, let them shuffle to their heart's content, and when they hand it back, replace the card.

And that's it, nothing more to it. 😉

Best regards and happy magic!!!