There is a verbal technique used in mentalism that doesn't fool anyone except the mentalist himself. And that is the following sentence structure used in a fishing procedure:
It wasn't a black card, was it?
Mentalists will claim that regardless of if the person is thinking of a red card or a black card, they will interpret this sentence as a "hit." No. They won't. They will think of it as exactly what it is: a question.
I noticed this a few years ago while watching a very good mentalist do some fishing.
Performer: "It's a high card."
Spectator: [Smiles] "Yes..."
Performer: "It's odd."
Spectator: [Crinkles her eyes.] "How are you doing this?"
Performer: "It's not a black card, is it?"
Spectator: "No, it's red."
Performer: "I thought so."
Spectator: [No reaction.]
Then I started noticing it in other people's routines as well. It never gets the reaction of a hit. And it dawned on me that of course it doesn't, because that's not how it comes off to the spectator.
If we were married and you started putting on your coat one evening and I said, "You're not going out, are you?" That is the same as me saying, "Are you going out?" Those sentences mean the same thing. The former suggests maybe I have an opinion on what I would like the answer to be, but it doesn't suggest any knowledge about your actual intent.
If you don't believe this sentence structure is only said in the context of not knowing, rather than knowing, try to put an obviously declarative sentence into the same structure and see how stupid it sounds.
"I'm not wearing a red shirt, am I?"
Of course there is a way to punctuate that statement so it is declarative. If you say:
"It's not a black card. Is it?" And you say it without an upward inflection at the end. Then that does mean "It's not a black card." But that sentence now has a definite meaning and doesn't suit your purpose.
I think the reason we think it's considered a hit is because the spectator doesn't say, "No, you're wrong." But of course they don't say you're wrong. You've just asked a question and not made a statement, how could you be wrong?
I don't really have an all-purpose alternative for this -- it would depend on the actual routine you were doing. I'm guessing in most circumstances it would be better to just simply say straight out, "It's a black card" (for example). You'll be right half the time. The other half of the time you will be wrong, of course, but often in these routines, once you're wrong you know exactly what the person is thinking. And even if you don't, you can take the miss and use it as an opportunity to change tactics. So maybe you say things aren't coming through clear enough reading their mind so instead you want to try and read their aura instead (or whatever nonsense you like to use). It's not an ideal solution, obviously, but if my options are to be right 50% of the time or to ask a weaselly-pseudo-statement-question 100% of the time, I will always choose the former.