The Jerx (previously) gave an audience at a magic show an app that let them tap when their suspicions were aroused.
The result was a "seismograph of audience suspicion that we could play along with the performance and see exactly where they were calling bullshit in their minds as they watched the performance." After sifting through the data, they concluded that "Suspicion is brought on by an unnecessary expenditure of energy on the part of the magician."
Keep this simple example in mind: If you went to the fanciest neighborhood in Los Angeles carrying a plastic Dollar Tree bag with a human head inside it, I don't think anyone would think anything of it as long as the bag was held down at your side by a relaxed, slack, arm.
On the other hand, if you walked around with the nicest bag filled with plans to build a soup kitchen for at-risk kittens, but held it up at shoulder level in a tight overhand grip, people would be like, "What's this dude's deal?" They'd be suspicious of why you were unnecessarily expending energy to hold a bag like that.
So let's bring it back to our example of the faro shuffle. Compared to a normal shuffle, it's a studied action that requires your attention (energy) and I think that's why it seemed questionable to a lay audience. They don't know what happened but the moment is questionable to them. And one of our goals should be to eliminate questionable moments because I think each one ends up reducing an audience's reaction by 5 or 10%. When we replaced the faro for a complete deck switch done in the performer's case (with some motivation), it did not trigger people's suspicion. That notion will make card technicians furious. The idea that it might be better to switch decks altogether — out of view from the audience — than just do a faro. It seems ridiculous. But I have no ego wrapped up in this, I'm only concerned with the audience's response to things. And if a well executed switch slides by unnoticed whereas an equally well executed faro shuffle raises an eyebrow, I'm going to go with the switch.