I know this is about coin tricks. But I had a recent problem with watch loads because whoever the spec is on the side of the watch. They always seems to get a flash of the card as it goes in. So what I do now is to give them a little wink or talk over them as they try to speak/expose.

I once was working a group and someone was giving me a hard time. He was saying out loud how he thought it was done, and it was a big distraction for everyone. I had to stop a couple of times and look his way as if to say, are you done now? I finally asked the group out loud, "By a show of hands, who wants to have a good time and enjoy the show". Then I looked at him and said, "The group has spoken. So please just sit back, relax, and stop trying to ruin everyone's fun."He apologized. Don't know if this would work every time, but I had the crowd on my side.