Your missing the point a little bit though. Why give them a needless reason to have a doubt about something? It's llike a little bug that gets in their brain and no matter how you try to explain it off that one thing puts the doubt there and it lingers.I really don't see what the big deal is if somebody wants to see the cards. Their freaking cards, let the person do what they want with them.
An example would be you as a magician watching another magician you hav'nt seen before. He does something and you glimps a move but you don't know what it was. Now you've lost the moment. There is that doupt bug in your brain. I hate this part as I'm usually not looking for it because personally I rather enjoy the moment when it comes.
I almost always got asked when using customs. I've tried everything from saying they are just a better quality deck that I can get more use out of, to spreading them to show the fronts and backs and saying they are normal. The problem is I should'nt have to. Thats not where I want the attention anyway. Mostly due in part to their beautiful designs it gets their brain thinki ng about questions. Then the doubt bug comes and eats their brain and they miss out on the moment.