I have his problem sometimes and there are certain thins i do in differnt situations
I either just don't give them the card to hold, and put it on the table insted. then ill tell thme to put their hand on top. Thats if they try to sneek in a peek, becasue then it's harder for them to try and look at the card.
If they ask to se the card and i wasn't prepared would say "oh, come on you really don't trust me?" as i take the card back, put it back on top of the deck adn do the double aain.
If i know there probably going to ask that from past experience with that person, i'll do the double, then confrim with them that's the card i'm putting in their hand by saing "Ok, your card the three of spades, right?"..."yes...'Okay, so the three is without doubt going into your hand," and i slowly turn the card over and put it in their hand.
Or, if i'm positive they will ask, ill actually putt that card in their hand. They will ask to see it, then you look annoyed. say "dude come on, don't ruin the trick, but yes this one time, look at it. My god..." take the card back (do a body flip over for the top card) put it on top and do the doble. They won't ask to see it again.